ENZYME

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Natural

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Bio-Energy Enzyme Sdn Bhd

Testimonial by Max Yong

I have a fairly hectic lefestyle. I work long hours, I'm a smoker and my meal is irregular. In order to keep myself healthy and energetic all the time, I have to take food supplement. to improve vitality . I used to take MLM products like spirulina, multi-vitamins and Lingzi. Most of the MLM products are generally good but they are too expensive if you are purely a consumer and not an active MLM member. I would say a normal income person can never afford to consume the MLM products in long term. Hence, I have to seek alternative. I have tried many natural health food products and finally I found a product that is affordable, natural, pure and diabetic friendly that I would like to share with you - BIO-ENERGY ENZYME.

There are many types of enzyme products available in the market nowadays. When you choose an enzyme product, you must make sure that the product is manufactured by a manufacturer with GMP (Good Manufacturing Practice) certificate and not a back yard manufacturer. Thus, the quality of the product is assured. Imported or local product is immaterial as long as it is produced by a reliable manufacturer. 

Secondly, is the cost. Food supplement is a long term consumption product and therefore it has to be affordable in long run. Try to justify the price of the product you intend to buy. For instance, there are some VEGETABLE enzyme drinks in the market that are selling more than RM200 per bottle (525ml). Contrary, you can also find some low-priced enzyme that taste like fruit juice. No harm trying all the products to see the difference like what I have done.

Thirdly, be aware of some vinegar products that claimed to be enzyme. Don't be misled by them. A vinegar is a  vinegar. You can get a bottle of good quality vinegar at below RM30!

A good quality enzyme drinks shall be 100% pure, no water added, no colouring, no preservative and it must be fermented at least two years. Diabetic friendly or sugar free is a bonus! The taste will tell the duration of the fermentation. Naturally, the enzyme will contain some alcohol derived from the fermentation process which would not make you drunk unless you consume more than as prescribed.

I have been consuming BIO-ENERGY ENZYME for 6 months. I find myself more alert, more energetic, having better sleep and better digestion system. I find it better than all the products that I have tried before. I am glad to have found this food supplement that I think everyone should give this healthy and affordable product a try, especially for those busy people on the road.

This product is available in selective pharmacy outlets only. Kindly contact us for more information of the outlets.

Please help to share the goodness of this enzyme drinks with your friends and relatives if you find it  good for you.

Cheers.

Max Yong

Understanding Mulberry Fruit

FRUIT AS MEDICINE

Morus Fruit (Mulberry)

by Subhuti Dharmananda, Ph.D., Director, Institute for Traditional Medicine, Portland, Oregon

Morus fruit from Morus alba, the mulberry plant, is often called mulberry fruit. Although there are many species of Morus, the one grown in China is the white mulberry (alba = white). One of the primary uses of the plant is for raising silkworms, which utilize the leaves as their main food source. 

China has been producing silk since ancient times and remains one of the world's primary sources. The Chinese term for the mulberry plant is sang, and the fruits are known in China as sanshenzi or simply sangshen. The fruit is botanically called a sorosis, because it is formed by the consolidation of many flowers. It is juicy and has a sweet taste with some sourness that is more prominent in the less mature fruits. 

Mulberry fruit is classified in the modern Chinese Materia Medica as a blood tonic, and is listed along with herbs having similar traditional uses such as ho-shou-wu (Polygonum multiflorum, root), cooked rehmannia (Rehmannia glutinosa, root), ligustrum (Ligustrum lucidum, fruit) and lycium (Lycium chinensis, fruit). 

Traditionally, mulberry fruit has been used as a medicinal agent to nourish the yin and blood, benefit the kidneys, and treat weakness, fatigue, anemia, and premature graying of hair. It is also used utilized to treat urinary incontinence, tinnitus, dizziness, and constipation in the elderly and the anemic. 

The dominant taste of the ripe fruit is sweet but usually somewhat bland, due to the high water content and low level of other flavoring ingredients, but a richer flavor develops if the fruit is dried; it can then be used as a raisin substitute. In recent years, with considerable work on cultivating the mulberry plants under various conditions, mulberry enzyme has been commercially produced as a health beverage, and it has become very popular in China, Japan, and Korea.

The mulberry fresh fruit constituents:-

Water: 85-88%
Carbohydrate (sugars, mainly glucose and fructose, producing the sweet taste): 7.8-9.2%
Protein: 0.4-1.5%
Fat (mainly fatty acids, such as linoleic, stearic, and oleic acids in the seeds): 0.4-0.5%
Free acids (mainly malic acid, producing the sour taste): 1.1-1.9%
Fiber: 0.9-1.4%
Minerals: 0.7-0.9%

You probably never heard about mulberry enzyme drinks until now. You may know silkworms, which eat mulberry leaves and spin cocoons. Mulberry leaves are always used to feed silkworm and mulberry fruit is usually discarded. The mulberry enzyme drinks enhance your health, such as yin nourishing, enriching the blood, tonifying the liver and kidney, calming the nerves, promoting the metabolism of alcohol, balancing internal secretions, and enhancing immunity. 

Nutritious and Bright

Mulberry is a kind of nourishing tonic medicine that can broadly be used to cure some debility symptoms when used with other restoratives. The person who has symptoms such as anemia, dizziness, or low libido, can take mulberry enzyme to build up health. An electuary, made from a prescription of mulberry with medlar, ligustrum, and schizandra, can nourish and enrich the blood; the wine made by immersing the mulberry in rice wine or grape wine, is a medicament for weakness after diseases that can also be used to tonify masculine vitality and benefit overall vitality.

Mulberry can nourish and promote production of body fluid. The person who has body fluid deficiency often feels their mouth parched and tongue scorched. When mulberry is ripe in the summer, a person can take one ounce every day. This product has a faint scent and sweet taste, suitable for people of all ages. Brew water to take the dry fruit, using 10 grams each time. The person who has dry eyes and uses their eyes a lot during work can drink mulberry enzyme, which can nourish the body fluid and strengthen sight. 

Mulberry contains plentiful nutritious elements, such as minerals and vitamins; it can cure chronic diseases of the digestive tract, promote gastric juice secretion, strengthen the ability for digesting and assimilating, improve the appetite, and eliminate abdominal distention and constipation. Mulberry is suitable also for chronic gastritis and chronic hepatitis.

Nourishing Blood and Blacken Hair
 

Mulberry has the function of nourishing blood. If the person who has anemia, pallor, dizziness, insomnia, and heart-palpitations regularly takes mulberry juice or enzyme, they will experience good effects. Women who have the above symptoms after childbirth, or anyone after a long-time sickness or after a major operation, can take mulberry frequently as a restorative. Compounding with other herbs to make Wuchang, mulberry is combined with tang-kuei, ligustrum, and rehmannia. 

A prescription or compound such as Wuchang can nourish blood, blacken hair, and help grow hair. Those who experience premature aging, such as graying hair and impotence, can take mulberry often. The pill, electuary, and wine all have high efficacy. The effect will be better for blackening hair and beautifying when it is combined with tang-kuei, ho-shou-wu, and drynaria. The mulberry juice can also be applied topically to the head to promote healthy hair growth.

HOW DOES MORUS FRUIT PRODUCE MEDICINAL EFFECTS?

The Chinese Materia Medica features numerous materials that are used as foods, including grains (wheat, millet, etc.), fruits (jujube, walnut), beans (soybeans, mung beans), and meats (oyster, pork). From the perspective of Western medicine, these are all useful as nutrient sources with obvious value to those suffering from various nutrient deficiencies, but they are usually not considered to have a therapeutic value. On the other hand, it is found by modern research that some foods contain additional non-nutrient ingredients that can have a distinct health impact. 

A good example is the isolation and characterization of isoflavones from soybeans. Soy is considered an excellent source of protein, and also a source of vitamins (especially vitamin E in its oil); the isoflavones, if consumed in sufficient quantity, can have a significant hormone-like action.

Though not studied intensively, mulberry fruits appear to contain one main class of non-nutrient active constituents, which are the anthocyanins. In particular, it is known to contain cyanin (the structure presented here), which contributes the red pigment that gives the fruit a red to purple color. The content in ripe fruits is about 0.2%; an ounce of fruit would provide about 60 mg anthocyanins. The dried fruits are used in doses of 9-15 grams per day in decoction, and this can yield about 90-150 mg of anthocyanins. In Chinese diets, this component may have been low, in which case, such herbal supplements (decoctions or juices) can be an important source.

In the U.S. today, with its rich resources in fruits that contain anthoycanins, it is estimated that adults consume about 180-215 mg/day of these components. A particularly rich source is blueberries; other major sources are cherries, black currants, bilberries, and other fruits with red, blue, or purple color. Still, a substantial increase in intake of anthocyanins, such as through morus fruit in herb formulas or beverages, could bring the dosage to a range where it has a more notable health impact. Studies with anthocyanins in laboratory animals suggest antioxidant activity as a dominant feature, but also cardiovascular protection, immune enhancement, antiviral activity, and stress reduction as potential health benefits. 

One cannot be certain that all, or any, of the claimed benefits of consuming morus fruit are valid. However, if we assume that a health benefit was obtained, several considerations may help us understand the action of the fruit:

1. Deficiencies in Chinese diets may have contributed to those problems mentioned as being remedied by morus fruit, such as anemia, constipation, premature graying of hair, etc. While morus fruit contains some nutrients (e.g., small amounts of calcium, iron, vitamin C, and B-vitamins), the anthocyanins may have improved blood circulation and other body functions to alleviate some symptoms that arise under the deficiency conditions. 
2. The specific benefits described in Chinese books may not be fully realized by people who have a good diet, because these individuals already receive adequate levels of the active components. However, other benefits or enhanced benefits still may be obtained by virtue of getting a higher dose of the active constituents.
3. Modern study of active constituents provides a basis for expanding the therapeutic benefit of herbs. For example, a patient who is prescribed an herb formula containing morus fruit might be told to additionally consume of other fruits (e.g., blue berries, cherries) or their juices. The black mulberry (Morus nigra) develops a richer tasting fruit than the white mulberry, and it can be consumed as a fresh fruit, juice, or jam. Thus, it is not necessary to rely solely on the Chinese herb ingredient to attain the desired results.
4. Chinese herb therapies (as complex formulas) may address a health problem by using a group of several herbs that have a similar end effect, but with different active components and different mechanisms. For example, a formula comprised of morus fruit, ho-shou-wu, rehmannia, and ligustrum may nourish blood, alleviate constipation, and have antioxidant and antiaging effects, but each herb contributes a different group of active components: anthocyanins, anthoquinones, iridoid glycosides, and oleanolic acid, respectively. Together, these may reduce adverse oxidative reactions, enhance circulation, alleviate inflammatory processes that yield systemic consequences, and improve the digestion and absorption of nutrients while enhancing the elimination of waste products of metabolism.

Mulberry cultivation areas in China

COMBINING OTHER HERBS WITH MORUS FRUIT

The following are examples of recommendations for use of morus fruit with other herbs to treat certain conditions:

1. For deficient yin and blood manifested as dizziness, vertigo, blurred vision, tinnitus, deafness, insomnia and early graying of hair, mulberry fruit is used with ho-shou-wu, ligustrum, and eclipta in the formula Shouwu Yanshou Dan. This combination can also be used for constipation in the elderly and for post-partum recovery. Ligustrum and eclipta together make a basic formula called Erzhi Wan, a well-known formula for yin deficiency with graying of the hair.
2. For thirst and dry mouth due to deficient body fluids or diabetes, manifesting as thirst with desire to drink, profuse urine, and lassitude, mulberry fruit is used with ophiopogon, ligustrum, and trichosanthes root; alternatively, one can combine it with ophiopogon, glehnia or adenophora, and yu-chu.
3. For constipation due to dryness in the intestines, mulberry fruit is used with black sesame seed, ho-shou-wu, and hemp seed (which can be substituted by flax seed).
4. For chronic arthritis, mulberry fruit is used with ho-shou-wu and chin-chiu (qinjiao).
5. For nervous stress, mulberry fruit is combined with schizandra and ligustrum.
6. For insomnia, mulberry fruit is used with zizyphus, tang-kuei, and hoelen (or fu-shen). Mulberry fruit can also be combined with rehmannia (both cooked and raw) to alleviate insomnia due to blood and yin deficiency.

In Chinese markets, mulberry is often provided in the form of a paste called sangshengao. The paste is mixed into hot water to make a tea to enrich the liver and kidney and sharpen the hearing and brighten the eyes. For this application, it can be combined with the traditional formula Yiqi Congming Tang, which is used for deficiencies in hearing and vision, particularly in the elderly who suffer from deficiency of yin with deficient heat.

APPENDIX: Food and Medicine Uses of Mulberries in Azerbaijan

Following is part of a story (The origin of mulberry trees by Farid Alakbarov and Iskandar Aliyev) that appeared in Azerbaijan International, Autumn 2000. 

Fresh mulberries are so fragile and perishable that they have not yet been grown commercially in the United States, making them very rare and sought after-especially in California. Restaurant chefs have been known to line up for hours at outdoor markets to buy these fashionable berries at $10 to $15 a pound. In the Los Angeles area, some Iranian immigrants have even resorted to planting their own mulberry orchards so that they will have easy access to their favorite fruit. But in Baku, the capital city of Azerbaijan, mulberry trees can be found in parks and lining streets and boulevards. It's one of the favorite fruits. 

This sweet, juicy berry is by no means a newcomer to Azerbaijan. By the Middle Ages, there were already many different types of mulberries in the region. There are three main species of mulberries-white, red and black-all of them widely cultivated throughout Azerbaijan. The white mulberry, in particular, grows in the forests stretched along the Kur, Araz, and Samur rivers.

To pick mulberries, a person-often a young boy-climbs the tree and shakes the branches, causing the fruit to drop onto a cloth or plastic sheet below. The berries are very delicate and therefore need to be handled carefully so that they don't break open-the stain won't wash out. Azerbaijanis don't grow mulberry trees just for their fruit, however. In the summer, residents in the villages around Baku used to sit and drink tea or play nard (backgammon) in the cool shade of mulberry trees. There is a square in the Old City (Ichari Shahar) that takes its name after the tree. Even a song has been written about the mulberry tree.

Today, mulberry trees (most frequently those bearing black fruit) line the streets of Baku and lend shade to courtyards. In the countryside, mulberry trees are often found in orchards and courtyards, along with a variety of other fruit trees like cherry, fig, pomegranate, apricot, apple and pear. Originally, male (fruitless) mulberry trees were planted along the streets and in the parks of Baku in order to provide shade and decoration. But somehow it happened that some female trees got planted as well. When their fruit becomes ripe each June, it tends to drop to the ground and stain the sidewalks. That's how you know it's mulberry season in Azerbaijan-that and kids' faces stained with the dark purple juice. When mulberries are no longer in season, Azerbaijanis still enjoy eating them in the form of mulberry syrup concentrates known as doshab and bakmaz. To make the syrup, mulberry juice is boiled until it has a consistency that's much like honey.  While this syrup makes a tasty sweet, it is also used as a medicine to protect against diseases of the liver, gall bladder, and heart. To treat gallbladder infections, one is supposed to drink 2 tablespoons of bakmaz dissolved in half a glass of water, then lie down in bed on his or her right side. The treatment should be taken on an empty stomach, half an hour before breakfast. Bakmaz is used to treat sore throats as well. Tut araghi, a potent liqueur made from mulberry juice, is another mulberry product that's very popular-not only Azerbaijan, but also in Georgia and Armenia. It's one of the national Azerbaijani versions of vodka. Some people believe that small doses of the drink protect against diseases of the stomach and heart.

Health Benefits of Mulberry

Mulberry is one of the nutrition treasures of alternative health medicine that has many health benefits to all who eat it. Mulberry contains fiber, calcium, phosphorus, potassium, magnesium, carbohydrates, iron and proteins essential to one's good health. The fruit is found mainly in the subtropical regions of Asia, Africa and the Americas and can be black, red, pink or white in color.

One benefit of Mulberry is that it contains anthocyanins. Anthocyanins are believed to contribute to the antioxidant properties of berries, and they are the reasons berries have their dark colors. At a 2007 symposium about the possible health benefits of berries, researchers presented theories that because berries contain anthocyanins they were able to: fight cancer, fight aging and neurological diseases, fight or control diabetes and fight against bacterial infections. Mulberry containing anthocyanin is therefore an antioxidant, which can provide all these benefits to those who eat them. Anthocyanins are also known to improve eyesight.

Mulberry juice is believed to be a good source of treating anemia and poor blood circulation. In Chinese medicine, people regularly mix Mulberry juice as a tonic and drink it to alleviate anemic symptoms and to improve their blood circulation. Mulberry also has the health benefit of soothing the nerves. When combined with Chinese schizandra and ligustrum, Mulberry is effective at soothing the nerves after a stressful day.

Mulberry is also a good source of nutrients that lower high blood pressure. The American Journal of Clinical Nutrition reports that eating just five ounces of mix berries a day can lower blood pressure, reducing the risk of blood clots and strokes.

Modern research done in France and Italy conclude that blood clotting and the degradation of collagen in the body leads to inflammation. Mulberry, like most berries, contains free radical scavengers that protect the body from degeneration. Specifically, Mulberry contains cyanidin 3-glucoside, which Epidemiological studies confirm reduces the risk of many degenerative diseases such as chronic arthritis and atherosclerosis. Thus, Mulberry fights against inflammation.

Cyanidin 3-glucoside according to the Journal of Medicinal Food also protects the body against cardiovascular disease and diabetes. Mulberry along with improving blood circulation, protecting the body against cardiovascular disease, also cures people who suffer from heart palpitations.

There are many health benefits of Mulberry. Mulberry has health benefits that have been proven in scientific research as well as health benefits that have survived the test of time in traditional Chinese medicine. But no matter to which medical belief you subscribe, what you can't deny is that the popularity and potential health benefits of berries are on the rise more than ever. So why not take a chance on this new wonder fruit and see if its benefits work for you.

Learn more about this author, Tommy Fassbender.

Mulberries are a fruit that is Asian, and these little vines of berries have several types of health benefits.

Mulberries have something in them, a compound known as anthocyanins. These antioxidant compounds are quite helpful in fighting off diseases such as certain cancers, diabetes, and various types of bacterium.

There is fiber that is contained in mulberries at 2.4 grams in a one cup serving size. Fiber is so essential to intestinal health and roughage, giving bulk to the stool. This nutrient also helps in preventing certain types of colon cancers as well as helping to lower cholesterol too.

Mulberries do have some potassium in them at 272 milligrams each serving. Potassium is needed to help us live since it controls heartbeats, regulates fluid levels in the body, and provides muscle energy too.

If you are deficient in iron, or have iron-deficiency anemia, eating mulberries provides you with 2.59 milligrams in a serving size. Another supporter of anemia and red blood cells is copper. Mulberries do have some of this vitamin, which helps your red blood cells to form hemoglobin as well as regulating the thyroid gland functions. Copper contained within the mulberry is 0.84 milligrams a serving.

Mulberries do have some folate at 8 micrograms per serving. Folate is a type of water-soluble vitamin which helps to regulate the homocystine levels in our body. Homocystine is a type of an amino acid that our body needs in order to help it function properly. Folate also is another type of vitamin which helps our health at the cellular levels.

Vitamin K is found in mulberries at 10 micrograms. Your blood needs this essential vitamin since it helps the clotting and bleeding factors to be normalized. Vitamin K also helps you process the calcium essential to your bones, and works to prevent hardening of the arteries too.

There is a bit of zinc in mulberries which totals 0.17 milligrams. Zinc is a mineral that actually activates many of the body's enzymes as well as helping build immunity, helping stress health, and making our sense of taste and smelling greater than if we didn't have zinc. Zinc also helps the skin to stay healthy.

There are also three supportive bone nutrients found in mulberries, phosphorus, magnesium, and calcium. Phosphorus helps our body to process calcium , and magnesium is what not only helps bone density, but it also plays roles in the regulation of blood sugar and blood glucose levels too. Calcium found in mulberries totals 55 milligrams, phosphorus 53 milligrams, and magnesium totals 25 milligrams.

Last but not least, other vitamins found in mulberries are niacin, which totals 868 milligrams and is cholesterol lowering, and Vitamin E which is a trace at 15 milligrams each. Vitamin E is a potent antioxidant, and helps skin health along with red blood cell health. It serves as protecting the skin from harmful UV rays, and has been known to help psoriasis to some degree.

Learn more about this author, Jennifer Kirkman.

Britannica Concise Encyclopedia: Enzyme

Substance that acts as a catalyst in living organisms, regulating the rate at which life's chemical reactions proceed without being altered in the process. Enzymes reduce the activation energy needed to start these reactions; without them, most such reactions would not take place at a useful rate. Because enzymes are not consumed, only tiny amounts of them are needed. Enzymes catalyze all aspects of cell metabolism, including the digestion of food, in which large nutrient molecules (including proteins, carbohydrates, and fats) are broken down into smaller molecules; the conservation and transformation of chemical energy; and the construction of cellular materials and components.

Almost all enzymes are proteins; many depend on a nonprotein cofactor, either a loosely associated organic compound (e.g., a vitamin; see coenzyme) or a tightly bound metal ion (e.g., iron, zinc) or organic (often metal-containing) group. The enzyme-cofactor combination provides an active configuration, usually including an active site into which the substance (substrate) involved in the reaction can fit. Many enzymes are specific to one substrate. If a competing molecule blocks the active site or changes its shape, the enzyme's activity is inhibited. If the enzyme's configuration is destroyed (see denaturation), its activity is lost.

Enzymes are classified by the type of reaction they catalyze: (1) oxidation-reduction, (2) transfer of a chemical group, (3) hydrolysis, (4) removal or addition of a chemical group, (5) isomerization (see isomer; isomerism), and (6) binding together of substrate units (polymerization). Most enzyme names end in -ase. Enzymes are chiral catalysts, producing mostly or only one of the possible stereoisomeric products (see optical activity). The fermentation of wine, leavening of bread, curdling of milk into cheese, and brewing of beer are all enzymatic reactions. The uses of enzymes in medicine include killing disease-causing microorganisms, promoting wound healing, and diagnosing certain diseases.

Food and Fitness: Eenzyme

Enzymes are proteins which act as biological catalysts accelerating specific chemical reactions, such as the digestion of food. Without enzymes, these reactions often require very high temperatures and pressures. Although enzymes take part in the reactions, they are not chemically altered by them. Consequently they are not used up and are required in relatively small concentrations. The body varies the concentration of a particular enzyme to regulate a specific activity; generally, the higher the enzyme concentration, the greater the rate of reaction.


Enzymes sometimes require additional, non-protein components to function properly; these are called cofactors. Many minerals and vitamins function as cofactors or coenzymes; deficiencies result in inefficient enzyme activity and ill health.

Enzymes work most effectively within narrow ranges of temperature and pH. Deviations cause the enzyme to change shape (denaturation) and to become less effective; this happens if the body overheats as a result of physical exertion or when lactic acid produced by anaerobic respiration lowers the pH of body fluids.

Food and Nutrition: Enzyme

A protein that catalyses a metabolic reaction, so increasing its rate. Enzymes are specific for both the compounds acted on (the substrates) and the reactions carried out. Because of this, enzymes extracted from plants, animals, or micro-organisms, or those produced by genetic manipulation are widely used in the chemical, pharmaceutical, and food industries (e.g. chymosin in cheese making, maltase in beer production, for synthesis of vitamin C and citric acid).


Because they are proteins, enzymes are permanently inactivated by heat, strong acid or alkali, and other conditions which cause denaturation of proteins.

Many enzymes contain non-protein components which are essential for their function. These are known as prosthetic groups, coenzymes, or cofactors, and may be metal ions, metal ions in organic combination (e.g. haem in haemoglobin and cytochromes) or a variety of organic compounds, many of which are derived from vitamins. The (inactive) protein without its prosthetic group is known as the apo-enzyme, and the active assembly of protein plus prosthetic group is the holo-enzyme. See also enzyme activation assays.

World of the Body: Enzymes

Enzymes are most familiarly associated with digestion, as substances in the alimentary tract that are necessary for the breakdown of food into simpler stuffs that can be absorbed into the body proper. These are indeed important, but they are in a small minority among the vast population of the body's enzymes. They also differ from the majority in acting outside rather than inside the cells that make them.


All living cells are teeming with enzymes. The name comes from the Greek meaning ‘in leaven’ or yeast. They are proteins, synthesized in cells, which act as catalysts, causing all the body's chemical processes to advance with the necessary rapidity and completeness. Enzymes are ubiquitous in body cells and fluids, and they are specific — each enzyme is responsible for catalyzing one particular chemical process. Their existence and their function came to be recognized during the nineteenth century; understanding advanced with burgeoning twentieth-century biochemistry; and molecular biologists continue to elucidate their ultimate structure and mode of action, and the genes that make them.

The names and nature of enzymes

The naming of enzymes in most cases reveals their function; ‘-ase’ is added to the name either of the substance (the substrate) on which they act (like peptidase for those acting on peptides), or of the type of reaction induced (such as hydrolase, for those causing hydrolysis, the splitting of a substance with addition of water, or transferase, for those moving some chemical group from one molecule to another). Some of the first enzymes to be discovered have unique names, such as pepsin in the stomach, and trypsin from the pancreas, which are both proteinases.

So what sort of proteins are they, and how do they function? With molecular masses of 10 000 to 1 000 000, enzymes are themselves large molecules, but some also exist in larger complexes that facilitate a sequence of changes. An enzyme molecule is a ‘globular’ protein that has an area on its surface to which can be bound only the specific substrate that the enzyme is designed to accept. This binding leads to changes in both molecules that result in the formation of the required product, and restoration of the enzyme molecule to its original state, ready to take on another substrate molecule. With progressively higher concentrations of substrate the rate of product yield increases, but the increment in rate diminishes as it approaches a maximum at a certain substrate concentration; beyond this point only an increase in the concentration of the enzyme itself can accelerate the process. This behaviour is consistent with progressive occupation of binding sites on all available enzymes, until they are all functioning at a maximal turnover rate.

Range and sites of enzyme function

Enzymes operate at every stage of life. Even the head of the sperm releases an enzyme that dissolves its path through the outer covering of the ovum to reach and penetrate it. Cell division in the embryo and throughout life involves replication of the DNA that carries the genetic information. A series of specific enzymes is needed for this, to unwind the double helix, to replicate it by the synthesis of new strands, and to put it and the new pairs back together again — whilst other enzymes meanwhile supply energy by the breakdown of adenosine triphosphate (ATP). Yet others are involved in the formation of messenger RNA and in all subsequent synthesis of proteins in a cell that results from the genetic coding.

Enzymes implement every event in the internal life of every cell in the body, and in its interaction with its environment. Each enzyme, or chain of enzymes acting in rapid sequence, has a specific function. There are those that are necessary for respiration and energy production; for transport mechanisms across the cell membrane and between internal components; for modifications of cellular metabolism in response to hormones; and for any specialized activity, including secretion by glandular cells, contraction by muscle cells, synthesis, release, and reuptake of neurotransmitters by nerve cells. The continual potential damage to tissues by the generation of free radicals is crucially limited by the body's antioxidant enzymes.

All cells have enzymes in their membrane, in the cytoplasm, and in the organelles within them. Those at the heart of cellular metabolism are the complex sequence of respiratory enzymes in the mitochondria that make possible the utilization of oxygen for the conversion of nutrient substrates to carbon dioxide and water, synthesis of ATP, and its breakdown for release of energy.

Cell membranes are furnished with ‘sodium pumps’ — protein molecules spanning the cell membrane that pump sodium ions out and potassium ions in. Facing inwards is an enzyme site that binds and breaks down ATP to supply the energy for pumping. Other enzyme molecules in the cell membrane may have, in addition to a site for substrate-binding, another that acts as receptor for a ‘messenger’ that activates the catalytic process: for example, the insulin receptor spans the cell membrane of muscle or fat cells; its outer site binds insulin, and its inner site handles the first of a series of enzyme-catalyzed reactions inside the cell that result in the several effects of insulin.

At synapses between nerves, and at neuromuscular junctions, enzymes are present that break down redundant neurotransmitters, preventing persistence of their effects. An example is acetylcholinesterase, found in the synaptic clefts on motor end plates in skeletal muscle, which hydrolyses excess acetylcholine, the neurotransmitter released by the motor nerve terminals.

Within skeletal muscle fibres, the enzymes vary according to their type of metabolism: whether it is predominantly aerobic (utilizing oxygen: ‘slow’ or ‘red’ muscle) or anaerobic (‘fast’ or ‘pale’ muscle). The sequence of events leading from activation of a muscle fibre by neurotransmitter, to contraction by means of interaction between myosin and actin filaments, depends on enzymes at every stage.

Enzymes in the blood

In the circulating blood there are enzymes both inside the blood cells, and outside in the plasma. Blood cells, in common with all cells, have the necessary enzymes for membrane transport and energy production. White blood cells have respiratory enzymes for aerobic metabolism, and others suited to their particular functions. Red blood cells are without mitochondria and respire anaerobically, so have enzymes appropriate to anaerobic glycolysis. Important for their function in whole-body respiratory gas exchange, they contain carbonic anhydrase, which promotes the uptake from the tissues of carbon dioxide and its carriage in the blood as bicarbonate, by catalyzing its combination with water to form carbonic acid, and its release in the lungs by this reaction in reverse.

Some enzymes exist as pro-enzymes or zymogens; they require some molecular change to be triggered into their active forms. These include proteins in the plasma that are involved in blood clotting: prothrombin is synthesized in the liver, and becomes thrombin when clotting is activated, and plasminogen can come into action as plasmin, a clot-dissolving enzyme. In the stomach, pepsinogen is secreted, and activated into pepsin by the acid that is secreted at the same site.

Enzymes that are normally secreted only into the gut or inside cells may, in pathological conditions, appear in significant quantities in the plasma, so that their measurement may be clinically useful. Examples are digestive enzymes that leak into the blood in acute pancreatitis, and creatine kinase, an enzyme from muscle tissue, that can appear in skeletal muscle disorders or, along with other intracellular enzymes, after a coronary thrombosis resulting in breakdown of some of the cardiac muscle.

Conditions for enzyme activity

All enzymes need the right environment for effective function, notably an optimal acidity, which differs in accordance with the site at which a particular enzyme acts (for example, more acidic inside cells than outside, and, for digestive enzymes, acidic in the stomach and alkaline in the duodenum). Like any chemical reactions, the rate of those that are catalyzed by enzymes varies with temperature. Local heat generation, for example in exercising muscle, enhances all such reactions within it. Likewise, whole-body metabolic rate increases in fever and decreases in hypothermia, because of the effect on all enzyme-catalyzed reactions. Extremes of pH or temperature irreversibly abolish enzyme activity, and so also do some substances that bind to the active sites of particular enzymes. These include an organophosphate ‘nerve gas’ that blocks acetylcholinesterase (causing persistent accumulation of acetylcholine at neuromuscular junctions, and thus uncontrollable muscle contraction). Poisoning by cyanide is due to blocking an essential enzyme in mitochondria and so fatally preventing all tissue respiration.

Medical applications

It is possible to inhibit the action of an enzyme without destroying it, and this has important therapeutic implications. There are substances that compete with the natural substrate for binding to an enzyme by having a similar structure, and others that act on other components of the enzyme molecule, preventing its ability to catalyze. Acetylcholinesterase inhibition is again an example — though in this context useful and reversible — in the treatment of the condition of myasthenia gravis, when the receptors on muscles cells for acetylcholine are deficient; the similar molecular structure of neostigmine allows it to bind to the enzyme, preventing binding and breakdown of acetylcholine; this can then accumulate sufficiently to enhance neuromuscular transmission. Drugs are used similarly to reverse the neuromuscular blockade deliberately induced during general anaesthesia. A different and important medical application of enzyme inhibition is in the use of antibiotics that block enzymes in microorganisms that are essential for their life or growth.

There are also many necessary co-enzymes, or co-factors for enzymes — organic non-protein molecules, smaller than the enzymes themselves, which either enhance or are necessary for the enzyme's activity. These again are widespread throughout the body, and are of many different molecular structures. Some require for their synthesis small amounts of essential substances from the diet. This is the basis of the need for the vitamins of the B group — they provide components for co-enzymes which could not otherwise be made in the body. Ions of several metals are also essential as co-factors, as well as for incorporation in some enzyme molecules themselves.



— Sheila Jennett

Science of Everyday Things: Enzymes

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Concept


Enzymes are biological catalysts, or chemicals that speed up the rate of reaction between substances without themselves being consumed in the reaction. As such, they are vital to such bodily functions as digestion, and they make possible processes that normally could not occur except at temperatures so high they would threaten the well-being of the body. A type of protein, enzymes sometimes work in tandem with non-proteins called coenzymes. Among the processes in which enzymes play a vital role is fermentation, which takes place in the production of alcohol or the baking of bread and also plays a part in numerous other natural phenomena, such as the purification of wastewater.

How It Works

Amino Acids, Proteins, and Biochemistry

Amino acids are organic compounds made of carbon, hydrogen, oxygen, nitrogen, and (in some cases) sulfur bonded in characteristic formations. Strings of 50 or more amino acids are known as proteins, large molecules that serve the functions of promoting normal growth, repairing damaged tissue, contributing to the body's immune system, and making enzymes. The latter are a type of protein that functions as a catalyst, a substance that speeds up a chemical reaction without participating in it. Catalysts, of which enzymes in the bodies of plants and animals are a good example, thus are not consumed in the reaction.

Catalysts

In a chemical reaction, substances known as reactants interact with one another to create new substances, called products. Energy is an important component in the chemical reaction, because a certain threshold, termed the activation energy, must be crossed before a reaction can occur. To increase the rate at which a reaction takes place and to hasten the crossing of the activation energy threshold, it is necessary to do one of three things.

The first two options are to increase either the concentration of reactants or the temperature at which the reaction takes place. It is not always feasible or desirable, however, to do either of these things. Many of the processes that take place in the human body, for instance, normally would require high temperatures—temperatures, in fact, that are too high to sustain human life. Imagine what would happen if the only way we had of digesting starch was to heat it to the boiling point inside our stomachs! Fortunately, there is a third option: the introduction of a catalyst, a substance that speeds up a reaction without participating in it either as a reactant or as a product. Catalysts thus are not consumed in the reaction. Enzymes, which facilitate the necessary reactions in our bodies without raising temperatures or increasing the concentrations of substances, are a prime example of a chemical catalyst.

The Discovery of Catalysis

Long before chemists recognized the existence of catalysts, ordinary people had been using the chemical process known as catalysis for numerous purposes: making soap, fermenting wine to create vinegar, or leavening bread, for instance. Early in the nineteenth century, chemists began to take note of this phenomenon. In 1812 the Russian chemist Gottlieb Kirchhoff (1764-1833) was studying the conversion of starches to sugar in the presence of strong acids when he noticed something interesting.

When a suspension of starch (that is, particles of starch suspended in water) was boiled, Kirchhoff observed, no change occurred in the starch. When he added a few drops of concentrated acid before boiling the suspension, however, he obtained a very different result. This time, the starch broke down to form glucose, a simple sugar (see Carbohydrates), whereas the acid—which clearly had facilitated the reaction—underwent no change. In 1835 the Swedish chemist Jöns Berzelius (1779-1848) provided a name to the process Kirchhoff had observed: catalysis, derived from the Greek words kata ("down") and lyein ("loosen"). Just two years earlier, in 1833, the French physiologist Anselme Payen (1795-1871) had isolated a material from malt that accelerated the conversion of starch to sugar, for instance, in the brewing of beer.

The renowned French chemist Louis Pasteur (1822-1895), who was right about so many things, called these catalysts ferments and pronounced them separate organisms. In 1897, however, the German biochemist Eduard Buchner (1860-1917) isolated the catalysts that bring about the fermentation of alcohol and determined that they were chemical substances, not organisms. By that time, the German physiologist Willy Kahne had suggested the name enzyme for these catalysts in living systems.

Substrates and Active Sites

Each type of enzyme is geared to interact chemically with only one particular substance or type of substance, termed a substrate. The two parts fit together, according to a widely accepted theory introduced in the 1890s by the German chemist Emil Fischer (1852-1919), as a key fits into a lock. Each type of enzyme has a specific three-dimensional shape that enables it to fit with the substrate, which has a complementary shape.

The link between enzymes and substrates is so strong that enzymes often are named after the substrate involved, simply by adding ase to the name of the substrate. For example, lactase is the enzyme that catalyzes the digestion of lactose, or milk sugar, and urease catalyzes the chemical breakdown of urea, a substance in urine. Enzymes bind their reactants or substrates at special folds and clefts, named active sites, in the structure of the substrate. Because numerous interactions are required in their work of catalysis, enzymes must have many active sites, and therefore they are very large, having atomic mass figures as high as one million amu. (An atomic mass unit, or amu, is approximately equal to the mass of a proton, a positively charged particle in the nucleus of an atom.)

Suppose a substrate molecule, such as a starch, needs to be broken apart for the purposes of digestion in a living body. The energy needed to break apart the substrate is quite large, larger than is available in the body. An enzyme with the correct molecular shape arrives on the scene and attaches itself to the substrate molecule, forming a chemical bond within it. The formation of these bonds causes the breaking apart of other bonds within the substrate molecule, after which the enzyme, its work finished, moves on to another uncatalyzed substrate molecule.

Coenzymes

All enzymes belong to the protein family, but many of them are unable to participate in a catalytic reaction until they link with a non protein component called a coenzyme. This can be a medium-size molecule called a prosthetic group, or it can be a metal ion (an atom with a net electric charge), in which case it is known as a cofactor. Quite often, though, coenzymes are composed wholly or partly of vitamins. Although some enzymes are attached very tightly to their coenzymes, others can be parted easily; in either case, the parting almost always deactivates both partners.

The first coenzyme was discovered by the English biochemist Sir Arthur Harden (1865-1940) around the turn of the nineteenth century. Inspired by Buchner, who in 1897 had detected an active enzyme in yeast juice that he had named zymase, Harden used an extract of yeast in most of his studies. He soon discovered that even after boiling, which presumably destroyed the enzymes in yeast, such deactivated yeast could be reactivated. This finding led Harden to the realization that a yeast enzyme apparently consists of two parts: a large, molecular portion that could not survive boiling and was almost certainly a protein and a smaller portion that had survived and was probably not a protein. Harden, who later shared the 1929 Nobel Prize in chemistry for this research, termed the non protein a coferment, but others began calling it a coenzyme.

Real-Life Applications

The Body, Food, and Digestion

Enzymes enable the many chemical reactions that are taking place at any second inside the body of a plant or animal. One example of an enzyme is cytochrome, which aids the respiratory system by catalyzing the combination of oxygen with hydrogen within the cells. Other enzymes facilitate the conversion of food to energy and make possible a variety of other necessary biological functions. Enzymes in the human body fulfill one of three basic functions. The largest of all enzyme types, sometimes called metabolic enzymes, assist in a wide range of basic bodily processes, from breathing to thinking. Some such enzymes are devoted to maintaining the immune system, which protects us against disease, and others are involved in controlling the effects of toxins, such as tobacco smoke, converting them to forms that the body can expel more easily.

A second category of enzyme is in the diet and consists of enzymes in raw foods that aid in the process of digesting those foods. They include proteases, which implement the digestion of protein; lipases, which help in digesting lipids or fats; and amylases, which make it possible to digest carbohydrates. Such enzymes set in motion the digestive process even when food is still in the mouth. As these enzymes move with the food into the upper portion of the stomach, they continue to assist with digestion.

The third group of enzymes also is involved in digestion, but these enzymes are already in the body. The digestive glands secrete juices containing enzymes that break down nutrients chemically into smaller molecules that are more easily absorbed by the body. Amylase in the saliva begins the process of breaking down complex carbohydrates into simple sugars. While food is still in the mouth, the stomach begins producing pepsin, which, like protease, helps digest protein.

Later, when food enters the small intestine, the pancreas secretes pancreatic juice—which contains three enzymes that break down carbohydrates, fats, and proteins—into the duodenum, which is part of the small intestine. Enzymes from food wind up among the nutrients circulated to the body through plasma, a watery liquid in which red blood cells are suspended. These enzymes in the blood assist the body in everything from growth to protection against infection.

One digestive enzyme that should be in the body, but is not always present, is lactase. As we noted earlier, lactase works on lactose, the principal carbohydrate in milk, to implement its digestion. If a person lacks this enzyme, consuming dairy products may cause diarrhea, bloating, and cramping. Such a person is said to be "lactose intolerant," and if he or she is to consume dairy products at all, they must be in forms that contain lactase. For this reason, Lactaid milk is sold in the specialty dairy section of major supermarkets, while many health-food stores sell lactaid tablets.

Fermentation

Fermentation, in its broadest sense, is a process involving enzymes in which a compound rich in energy is broken down into simpler substances. It also is sometimes identified as a process in which large organic molecules (those containing hydrogen and carbon) are broken down into simpler molecules as the result of the action of microorganisms working anaerobically, or in the absence of oxygen. The most familiar type of fermentation is the conversion of sugars and starches to alcohol by enzymes in yeast. To distinguish this reaction from other kinds of fermentation, the process is sometimes termed alcoholic or ethanolic fermentation.

At some point in human prehistory, humans discovered that foods spoil, or go bad. Yet at the dawn of history—that is, in ancient Sumer and Egypt—people found that sometimes the "spoilage" (that is, fermentation) of products could have beneficial results. Hence the fermentation of fruit juices, for example, resulted in the formation of primitive forms of wine. Over the centuries that followed, people learned how to make both alcoholic beverages and bread through the controlled use of fermentation.

Alcoholic Beverages

In fermentation, starch is converted to simple sugars, such as sucrose and glucose, and through a complex sequence of some 12 reactions, these sugars then are converted to ethyl alcohol (the kind of alcohol that can be consumed, as opposed to methyl alcohol and other toxic forms) and carbon dioxide. Numerous enzymes are needed to carry out this sequence of reactions, the most important being zymase, which is found in yeast cells. These enzymes are sensitive to environmental conditions, such that when the concentration of alcohol reaches about 14%, they are deactivated. For this reason, no fermentation product (such as wine) can have an alcoholic concentration of more than about 14%. Stronger alcoholic beverages, such as whisky, are the result of another process, distillation.

The alcoholic beverages that can be produced by fermentation vary widely, depending primarily on two factors: the plant that is fermented and the enzymes used for fermentation. Depending on the materials available to them, various peoples have used grapes, berries, corn, rice, wheat, honey, potatoes, barley, hops, cactus juice, cassava roots, and other plant materials for fermentation to produce wines, beers, and other fermented drinks. The natural product used in making the beverage usually determines the name of the synthetic product. Thus, for instance, wine made with rice—a time-honored tradition in Japan—is known as sake, while a fermented beverage made from barley, hops, or malt sugar has a name very familiar to Americans: beer. Grapes make wine, but "wine" made from honey is known as mead.

Other Foods

Of course, ethyl alcohol is not the only useful product of fermentation or even of fermentation using yeast; so, too, are baked goods, such as bread. The carbon dioxide generated during fermentation is an important component of such items. When the batter for bread is mixed, a small amount of sugar and yeast is added. The bread then rises, which is more than just a figure of speech: it actually puffs up as a result of the fermentation of the sugar by enzymes in the yeast, which brings about the formation of carbon dioxide gas. The carbon dioxide gives the batter bulkiness and texture that would be lacking without the fermentation process. Another food-related application of fermentation is the production of one processed type of food from a raw, natural variety. The conversion of raw olives to the olives sold in stores, of cucumbers to pickles, and of cabbage to sauerkraut utilizes a particular bacterium that assists in a type of fermentation.

Industrial Applications

There is even ongoing research into the creation of edible products from the fermentation of petroleum. While this may seem a bit far-fetched, it is less difficult to comprehend powering cars with an environmentally friendly product of fermentation known as gasohol. Gasohol first started to make headlines in the 1970s, when an oil embargo and resulting increases in gas prices, combined with growing environmental concerns, raised the need for a type of fuel that would use less petroleum. A mixture of about 90% gasoline and 10% alcohol, gasohol burns more cleanly that gasoline alone and provides a promising method for using renewable resources (plant material) to extend the availability of a nonrenewable resource (petroleum). Furthermore, the alcohol needed for this product can be obtained from the fermentation of agricultural and municipal wastes.

The applications of fermentation span a wide spectrum, from medicines that go into people's bodies to the cleaning of waters containing human waste. Some antibiotics and other drugs are prepared by fermentation: for example, cortisone, used in treating arthritis, can be made by fermenting a plant steroid known as diosgenin. In the treatment of wastewater, anaerobic, or non-oxygen-dependent, bacteria are used to ferment organic material. Thus, solid wastes are converted to carbon dioxide, water, and mineral salts.

Where to Learn More

Asimov, Isaac. The Chemicals of Life: Enzymes, Vitamins, Hormones. New York: Abelard-Schulman, 1954.

"Enzymes: Classification, Structure, Mechanism." Washington State University Department of Chemistry (Web site). <http://www.chem.wsu.edu/Chem102/102-EnzStrClassMech.html>.

"Enzymes." HordeNet: Hardy Research Group, Department of Chemistry, The University of Akron (Web site). <http://ull.chemistry.uakron.edu/genobc/Chapter_20/>.

Fruton, Joseph S. A Skeptical Biochemist. Cambridge, MA: Harvard University Press, 1992.

"Introduction to Enzymes." Worthington Biochemical Corporation (Web site). <http://www.worthingtonbiochem.com/introBiochem/introEnzymes.html>.

Kornberg, Arthur. For the Love of Enzymes: The Odyssey of a Biochemist. Cambridge, MA: Harvard University Press, 1989.

"Milk Makes Me Sick: Exploration of the Basis of Lactose Intolerance." Exploratorium: The Museum of Science, Art, and Human Perception (Web site). <http://www.exploratorium.edu/snacks/milk_makes-me_sick/>.

Wikipedia: Enzyme

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What Is Enzyme?

Enzymes are proteins that catalyze (i.e., increase the rates of) chemical reactions.[1][2] In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, called the products. Almost all processes in a biological cell need enzymes to occur at significant rates. Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.


Like all catalysts, enzymes work by lowering the activation energy (Ea‡) for a reaction, thus dramatically increasing the rate of the reaction. Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions. However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions.[3] A few RNA molecules called ribozymes also catalyze reactions, with an important example being some parts of the ribosome.[4][5] Synthetic molecules called artificial enzymes also display enzyme-like catalysis.[6]

Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease enzyme activity; activators are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. Activity is also affected by temperature, chemical environment (e.g., pH), and the concentration of substrate. Some enzymes are used commercially, for example, in the synthesis of antibiotics. In addition, some household products use enzymes to speed up biochemical reactions (e.g., enzymes in biological washing powders break down protein or fat stains on clothes; enzymes in meat tenderizers break down proteins, making the meat easier to chew).

Etymology and History


As early as the late 18th and early 19th centuries, the digestion of meat by stomach secretions[7] and the conversion of starch to sugars by plant extracts and saliva were known. However, the mechanism by which this occurred had not been identified.[8]


In the 19th century, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur came to the conclusion that this fermentation was catalyzed by a vital force contained within the yeast cells called "ferments", which were thought to function only within living organisms. He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells."[9]

In 1877, German physiologist Wilhelm Kühne (1837–1900) first used the term enzyme, which comes from Greek ενζυμον, "in leaven", to describe this process.[10] The word enzyme was used later to refer to nonliving substances such as pepsin, and the word ferment was used to refer to chemical activity produced by living organisms.

In 1897, Eduard Buchner submitted his first paper on the ability of yeast extracts that lacked any living yeast cells to ferment sugar. In a series of experiments at the University of Berlin, he found that the sugar was fermented even when there were no living yeast cells in the mixture.[11] He named the enzyme that brought about the fermentation of sucrose "zymase".[12] In 1907, he received the Nobel Prize in Chemistry "for his biochemical research and his discovery of cell-free fermentation". Following Buchner's example, enzymes are usually named according to the reaction they carry out. Typically, to generate the name of an enzyme, the suffix -ase is added to the name of its substrate (e.g., lactase is the enzyme that cleaves lactose) or the type of reaction (e.g., DNA polymerase forms DNA polymers).[13]

Having shown that enzymes could function outside a living cell, the next step was to determine their biochemical nature. Many early workers noted that enzymatic activity was associated with proteins, but several scientists (such as Nobel laureate Richard Willstätter) argued that proteins were merely carriers for the true enzymes and that proteins per se were incapable of catalysis. However, in 1926, James B. Sumner showed that the enzyme urease was a pure protein and crystallized it; Sumner did likewise for the enzyme catalase in 1937. The conclusion that pure proteins can be enzymes was definitively proved by Northrop and Stanley, who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin. These three scientists were awarded the 1946 Nobel Prize in Chemistry.[14]

This discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography. This was first done for lysozyme, an enzyme found in tears, saliva and egg whites that digests the coating of some bacteria; the structure was solved by a group led by David Chilton Phillips and published in 1965.[15] This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail.

Structures and mechanisms

Enzymes are generally globular proteins and range from just 62 amino acid residues in size, for the monomer of 4-oxalocrotonate tautomerase,[16] to over 2,500 residues in the animal fatty acid synthase.[17] A small number of RNA-based biological catalysts exist, with the most common being the ribosome; these are referred to as either RNA-enzymes or ribozymes. The activities of enzymes are determined by their three-dimensional structure.[18] However, although structure does determine function, predicting a novel enzyme's activity just from its structure is a very difficult problem that has not yet been solved.[19]


Most enzymes are much larger than the substrates they act on, and only a small portion of the enzyme (around 3–4 amino acids) is directly involved in catalysis.[20] The region that contains these catalytic residues, binds the substrate, and then carries out the reaction is known as the active site. Enzymes can also contain sites that bind cofactors, which are needed for catalysis. Some enzymes also have binding sites for small molecules, which are often direct or indirect products or substrates of the reaction catalyzed. This binding can serve to increase or decrease the enzyme's activity, providing a means for feedback regulation.

Like all proteins, enzymes are long, linear chains of amino acids that fold to produce a three-dimensional product. Each unique amino acid sequence produces a specific structure, which has unique properties. Individual protein chains may sometimes group together to form a protein complex. Most enzymes can be denatured—that is, unfolded and inactivated—by heating or chemical denaturants, which disrupt the three-dimensional structure of the protein. Depending on the enzyme, denaturation may be reversible or irreversible.

Structures of enzymes in complex with substrates or substrate analogs during a reaction may be obtained using Time resolved crystallography methods.

Specificity

Enzymes are usually very specific as to which reactions they catalyze and the substrates that are involved in these reactions. Complementary shape, charge and hydrophilic/hydrophobic characteristics of enzymes and substrates are responsible for this specificity. Enzymes can also show impressive levels of stereospecificity, regioselectivity and chemoselectivity.[21]


Some of the enzymes showing the highest specificity and accuracy are involved in the copying and expression of the genome. These enzymes have "proof-reading" mechanisms. Here, an enzyme such as DNA polymerase catalyzes a reaction in a first step and then checks that the product is correct in a second step.[22] This two-step process results in average error rates of less than 1 error in 100 million reactions in high-fidelity mammalian polymerases.[23] Similar proofreading mechanisms are also found in RNA polymerase,[24] aminoacyl tRNA synthetases[25] and ribosomes.[26]

Some enzymes that produce secondary metabolites are described as promiscuous, as they can act on a relatively broad range of different substrates. It has been suggested that this broad substrate specificity is important for the evolution of new biosynthetic pathways.[27]

"Lock and key" model

Enzymes are very specific, and it was suggested by the Nobel laureate organic chemist Emil Fischer in 1894 that this was because both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another.[28] This is often referred to as "the lock and key" model. However, while this model explains enzyme specificity, it fails to explain the stabilization of the transition state that enzymes achieve.
 

Diagrams to show the induced fit hypothesis of enzyme action.In 1958, Daniel Koshland suggested a modification to the lock and key model: since enzymes are rather flexible structures, the active site is continually reshaped by interactions with the substrate as the substrate interacts with the enzyme.[29] As a result, the substrate does not simply bind to a rigid active site; the amino acid side chains which make up the active site are molded into the precise positions that enable the enzyme to perform its catalytic function. In some cases, such as glycosidases, the substrate molecule also changes shape slightly as it enters the active site.[30] The active site continues to change until the substrate is completely bound, at which point the final shape and charge is determined [31]. Induced fit may enhance the fidelity of molecular recognition in the presence of competition and noise via the conformational proofreading mechanism [32].

Mechanisms

Enzymes can act in several ways, all of which lower ΔG‡:[33]




Lowering the activation energy by creating an environment in which the transition state is stabilized (e.g. straining the shape of a substrate—by binding the transition-state conformation of the substrate/product molecules, the enzyme distorts the bound substrate(s) into their transition state form, thereby reducing the amount of energy required to complete the transition).

Lowering the energy of the transition state, but without distorting the substrate, by creating an environment with the opposite charge distribution to that of the transition state.

Providing an alternative pathway. For example, temporarily reacting with the substrate to form an intermediate ES complex, which would be impossible in the absence of the enzyme.

Reducing the reaction entropy change by bringing substrates together in the correct orientation to react. Considering ΔH‡ alone overlooks this effect.

Increases in temperatures speed up reactions. Thus, temperature increases help the enzyme function and develop the end product even faster. However, if heated too much, the enzyme’s shape deteriorates and only when the temperature comes back to normal does the enzyme regain its shape. Some enzymes like thermolabile enzymes work best at low temperatures.

Interestingly, this entropic effect involves destabilization of the ground state,[34] and its contribution to catalysis is relatively small.[35]

Transition State Stabilization


The understanding of the origin of the reduction of ΔG‡ requires one to find out how the enzymes can stabilize its transition state more than the transition state of the uncatalyzed reaction. Apparently, the most effective way for reaching large stabilization is the use of electrostatic effects, in particular, by having a relatively fixed polar environment that is oriented toward the charge distribution of the transition state.[36] Such an environment does not exist in the uncatalyzed reaction in water.

Dynamics and function


The internal dynamics of enzymes is linked to their mechanism of catalysis.[37][38][39] Internal dynamics are the movement of parts of the enzyme's structure, such as individual amino acid residues, a group of amino acids, or even an entire protein domain. These movements occur at various time-scales ranging from femtoseconds to seconds. Networks of protein residues throughout an enzyme's structure can contribute to catalysis through dynamic motions.[40][41][42][43] Protein motions are vital to many enzymes, but whether small and fast vibrations, or larger and slower conformational movements are more important depends on the type of reaction involved. However, although these movements are important in binding and releasing substrates and products, it is not clear if protein movements help to accelerate the chemical steps in enzymatic reactions.[44] These new insights also have implications in understanding allosteric effects and developing new drugs.


Allosteric modulation

Allosteric sites are sites on the enzyme that bind to molecules in the cellular environment. The sites form weak, noncovalent bonds with these molecules, causing a change in the conformation of the enzyme. This change in conformation translates to the active site, which then affects the reaction rate of the enzyme.[45] Allosteric interactions can both inhibit and activate enzymes and are a common way that enzymes are controlled in the body.[46]


Cofactors and coenzymes

Cofactors


Some enzymes do not need any additional components to show full activity. However, others require non-protein molecules called cofactors to be bound for activity.[47] Cofactors can be either inorganic (e.g., metal ions and iron-sulfur clusters) or organic compounds (e.g., flavin and heme). Organic cofactors can be either prosthetic groups, which are tightly bound to an enzyme, or coenzymes, which are released from the enzyme's active site during the reaction. Coenzymes include NADH, NADPH and adenosine triphosphate. These molecules transfer chemical groups between enzymes.[48]

An example of an enzyme that contains a cofactor is carbonic anhydrase, and is shown in the ribbon diagram above with a zinc cofactor bound as part of its active site.[49] These tightly bound molecules are usually found in the active site and are involved in catalysis. For example, flavin and heme cofactors are often involved in redox reactions.

Enzymes that require a cofactor but do not have one bound are called apoenzymes or apoproteins. An apoenzyme together with its cofactor(s) is called a holoenzyme (this is the active form). Most cofactors are not covalently attached to an enzyme, but are very tightly bound. However, organic prosthetic groups can be covalently bound (e.g., thiamine pyrophosphate in the enzyme pyruvate dehydrogenase). The term "holoenzyme" can also be applied to enzymes that contain multiple protein subunits, such as the DNA polymerases; here the holoenzyme is the complete complex containing all the subunits needed for activity.

Coenzymes

Coenzymes are small organic molecules that transport chemical groups from one enzyme to another.[50] Some of these chemicals such as riboflavin, thiamine and folic acid are vitamins (compounds which cannot be synthesized by the body and must be acquired from the diet). The chemical groups carried include the hydride ion (H-) carried by NAD or NADP+, the phosphate group carried by adenosine triphosphate, the acetyl group carried by coenzyme A, formyl, methenyl or methyl groups carried by folic acid and the methyl group carried by S-adenosylmethionine.


Since coenzymes are chemically changed as a consequence of enzyme action, it is useful to consider coenzymes to be a special class of substrates, or second substrates, which are common to many different enzymes. For example, about 700 enzymes are known to use the coenzyme NADH.[51]

Coenzymes are usually continuously regenerated and their concentrations maintained at a steady level inside the cell: for example, NADPH is regenerated through the pentose phosphate pathway and S-adenosylmethionine by methionine adenosyltransferase. This continuous regeneration means that even small amounts of coenzymes are used very intensively. For example, the human body turns over its own weight in ATP each day.[52]

Biological function
Enzymes serve a wide variety of functions inside living organisms. They are indispensable for signal transduction and cell regulation, often via kinases and phosphatases.[71] They also generate movement, with myosin hydrolysing ATP to generate muscle contraction and also moving cargo around the cell as part of the cytoskeleton.[72] Other ATPases in the cell membrane are ion pumps involved in active transport. Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies.[73] Viruses can also contain enzymes for infecting cells, such as the HIV integrase and reverse transcriptase, or for viral release from cells, like the influenza virus neuraminidase.


An important function of enzymes is in the digestive systems of animals. Enzymes such as amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines. Starch molecules, for example, are too large to be absorbed from the intestine, but enzymes hydrolyse the starch chains into smaller molecules such as maltose and eventually glucose, which can then be absorbed. Different enzymes digest different food substances. In ruminants which have herbivorous diets, microorganisms in the gut produce another enzyme, cellulase to break down the cellulose cell walls of plant fiber.[74]

Glycolytic enzymes and their functions in the metabolic pathway of glycolysisSeveral enzymes can work together in a specific order, creating metabolic pathways. In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the catalytic reaction, the product is then passed on to another enzyme. Sometimes more than one enzyme can catalyze the same reaction in parallel, this can allow more complex regulation: with for example a low constant activity being provided by one enzyme but an inducible high activity from a second enzyme.

Enzymes determine what steps occur in these pathways. Without enzymes, metabolism would neither progress through the same steps, nor be fast enough to serve the needs of the cell. Indeed, a metabolic pathway such as glycolysis could not exist independently of enzymes. Glucose, for example, can react directly with ATP to become phosphorylated at one or more of its carbons. In the absence of enzymes, this occurs so slowly as to be insignificant. However, if hexokinase is added, these slow reactions continue to take place except that phosphorylation at carbon 6 occurs so rapidly that if the mixture is tested a short time later, glucose-6-phosphate is found to be the only significant product. Consequently, the network of metabolic pathways within each cell depends on the set of functional enzymes that are present.

Control of activity


There are five main ways that enzyme activity is controlled in the cell.

Enzyme production (transcription and translation of enzyme genes) can be enhanced or diminished by a cell in response to changes in the cell's environment. This form of gene regulation is called enzyme induction and inhibition (see enzyme induction). For example, bacteria may become resistant to antibiotics such as penicillin because enzymes called beta-lactamases are induced that hydrolyse the crucial beta-lactam ring within the penicillin molecule. Another example are enzymes in the liver called cytochrome P450 oxidases, which are important in drug metabolism. Induction or inhibition of these enzymes can cause drug interactions.

Enzymes can be compartmentalized, with different metabolic pathways occurring in different cellular compartments. For example, fatty acids are synthesized by one set of enzymes in the cytosol, endoplasmic reticulum and the Golgi apparatus and used by a different set of enzymes as a source of energy in the mitochondrion, through β-oxidation.[75]

Enzymes can be regulated by inhibitors and activators. For example, the end product(s) of a metabolic pathway are often inhibitors for one of the first enzymes of the pathway (usually the first irreversible step, called committed step), thus regulating the amount of end product made by the pathways. Such a regulatory mechanism is called a negative feedback mechanism, because the amount of the end product produced is regulated by its own concentration. Negative feedback mechanism can effectively adjust the rate of synthesis of intermediate metabolites according to the demands of the cells. This helps allocate materials and energy economically, and prevents the manufacture of excess end products. The control of enzymatic action helps to maintain a stable internal environment in living organisms.

Enzymes can be regulated through post-translational modification. This can include phosphorylation, myristoylation and glycosylation. For example, in the response to insulin, the phosphorylation of multiple enzymes, including glycogen synthase, helps control the synthesis or degradation of glycogen and allows the cell to respond to changes in blood sugar.[76] Another example of post-translational modification is the cleavage of the polypeptide chain. Chymotrypsin, a digestive protease, is produced in inactive form as chymotrypsinogen in the pancreas and transported in this form to the stomach where it is activated. This stops the enzyme from digesting the pancreas or other tissues before it enters the gut. This type of inactive precursor to an enzyme is known as a zymogen.

Some enzymes may become activated when localized to a different environment (e.g. from a reducing (cytoplasm) to an oxidizing (periplasm) environment, high pH to low pH etc.). For example, hemagglutinin in the influenza virus is activated by a conformational change caused by the acidic conditions, these occur when it is taken up inside its host cell and enters the lysosome.[77]

Involvement in disease


Phenylalanine hydroxylase. Created from PDB 1KW0Since the tight control of enzyme activity is essential for homeostasis, any malfunction (mutation, overproduction, underproduction or deletion) of a single critical enzyme can lead to a genetic disease. The importance of enzymes is shown by the fact that a lethal illness can be caused by the malfunction of just one type of enzyme out of the thousands of types present in our bodies.

One example is the most common type of phenylketonuria. A mutation of a single amino acid in the enzyme phenylalanine hydroxylase, which catalyzes the first step in the degradation of phenylalanine, results in build-up of phenylalanine and related products. This can lead to mental retardation if the disease is untreated.[78]

Another example is when germline mutations in genes coding for DNA repair enzymes cause hereditary cancer syndromes such as xeroderma pigmentosum. Defects in these enzymes cause cancer since the body is less able to repair mutations in the genome. This causes a slow accumulation of mutations and results in the development of many types of cancer in the sufferer.

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