Originally Answered: what are Enzymes?
Enzyme, any one of many specialized organic substances, composed of polymers of amino acids, that act as catalysts to regulate the speed of the many chemical reactions involved in the metabolism of living organisms, such as digestion. The name enzyme was suggested in 1867 by the German physiologist Wilhelm Kühne (1837-1900); it is derived from the Greek phrase en zymē, meaning “in leaven.” Those enzymes identified now number more than 700.
Enzymes are classified into several broad categories, such as hydrolytic, oxidizing, and reducing, depending on the type of reaction they control. Hydrolytic enzymes accelerate reactions in which a substance is broken down into simpler compounds through reaction with water molecules. Oxidizing enzymes, known as oxidases, accelerate oxidation reactions; reducing enzymes speed up reduction reactions, in which oxygen is removed. Many other enzymes catalyze other types of reactions.
Individual enzymes are named by adding ase to the name of the substrate with which they react. The enzyme that controls urea decomposition is called urease; those that control protein hydrolyses are known as proteinases. Some enzymes, such as the proteinases trypsin and pepsin, retain the names used before this nomenclature was adopted.
II Properties of Enzymes
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As the Swedish chemist Jöns Jakob Berzelius suggested in 1823, enzymes are typical catalysts: they are capable of increasing the rate of reaction without being consumed in the process. See Catalysis.
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Some enzymes, such as pepsin and trypsin, which bring about the digestion of meat, control many different reactions, whereas others, such as urease, are extremely specific and may accelerate only one reaction. Still others release energy to make the heart beat and the lungs expand and contract. Many facilitate the conversion of sugar and foods into the various substances the body requires for tissue-building, the replacement of blood cells, and the release of chemical energy to move muscles.
Pepsin, trypsin, and some other enzymes possess, in addition, the peculiar property known as autocatalysis, which permits them to cause their own formation from an inert precursor called zymogen. As a consequence, these enzymes may be reproduced in a test tube.
As a class, enzymes are extraordinarily efficient. Minute quantities of an enzyme can accomplish at low temperatures what would require violent reagents and high temperatures by ordinary chemical means. About 30 g (about 1 oz) of pure crystalline pepsin, for example, would be capable of digesting nearly 2 metric tons of egg white in a few hours.
The kinetics of enzyme reactions differ somewhat from those of simple inorganic reactions. Each enzyme is selectively specific for the substance in which it causes a reaction and is most effective at a temperature peculiar to it. Although an increase in temperature may accelerate a reaction, enzymes are unstable when heated. The catalytic activity of an enzyme is determined primarily by the enzyme's amino-acid sequence and by the tertiary structure—that is, the three-dimensional folded structure—of the macromolecule. Many enzymes require the presence of another ion or a molecule, called a cofactor, in order to function.
As a rule, enzymes do not attack living cells. As soon as a cell dies, however, it is rapidly digested by enzymes that break down protein. The resistance of the living cell is due to the enzyme's inability to pass through the membrane of the cell as long as the cell lives. When the cell dies, its membrane becomes permeable, and the enzyme can then enter the cell and destroy the protein within it. Some cells also contain enzyme inhibitors, known as antienzymes, which prevent the action of an enzyme upon a substrate.
III Practical Uses of Enzymes
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Alcoholic fermentation and other important industrial processes depend on the action of enzymes that are synthesized by the yeasts and bacteria used in the production process. A number of enzymes are used for medical purposes. Some have been useful in treating areas of local inflammation; trypsin is employed in removing foreign matter
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