Enzymes or ferments are catalysts produced by living organisms that perform their function in the metabolism (v. PHYSIOLOGY) of living beings.
Like all catalysts, they do not alter the equilibrium state of a chemical system, but they modify the rate at which this equilibrium is reached; in other words, they accelerate (or retard) the speed of chemical reactions, and are not destroyed in the catalyzed reactions.
From a chemical standpoint, enzymes are protein substances, and often it is possible to distinguish within them a chemical group—particularly important in the function of the enzyme—which is called the coenzyme; many vitamins, such as the B-group vitamins, form part of coenzymes.
Most enzymes act within the cell itself, from which they are more or less easily detachable, but some enzymes are secreted by the cell to act outside it, though still for the benefit of the organism. Among the latter are the well-known enzymes that break down food substances in the digestive tract (digestion), released in the oral cavity (ptyalin), in the stomach (pepsin, chymosin), and in the intestine (trypsin, steapsin, amylopsin, etc.).
Enzymes make possible the hydrolytic and oxidative degradation of food fuel, which otherwise, at the temperature of living organisms, could occur only with extreme slowness; they also regulate this degradation so that the release of energy takes place in an orderly manner according to need, rather than tumultuously.
Enzymes are usually classified according to the reactions they catalyze; two major categories are distinguished: 1) hydrolases, or hydrolytic enzymes, which catalyze reactions leading to the breakdown of a complex molecule into simpler ones with the incorporation of a water molecule, such as the splitting of sucrose into glucose and fructose. 2) desmolases, or desmolytic enzymes, which serve to accelerate the breakdown of simpler molecules resulting from hydrolysis and the complete oxidation of organic substances into water and carbon dioxide. Particularly important in this category of enzymes are oxidases and dehydrogenases, which are oxidizing enzymes.
The mechanism of enzyme action consists in reducing or increasing the chemical inertia of the fermented substrate by means not always fully understood, but which generally lead to the formation of intermediate compounds between substrate and enzyme.