FERMENTS and FERMENTATION. — Ferments or enzymes are catalysts produced by living organisms that perform their function in the metabolism (v. FISIOLOGIA) of living beings.
Like all catalysts, they do not shift the state of equilibrium of a chemical system, but modify the speed at which that equilibrium is reached; in other words, they accelerate (or retard) the rate of chemical reactions, and are not destroyed in the catalysed reactions.
From the chemical point of view, f. are protein substances, and it is often possible to distinguish in them a chemical group, particularly important in the function of the f., which is called a coferment; many vitamins, such as the vitamins of group B, form part of coferments.
Most f. act within the cell itself, from which they can be detached more or less readily, but some f. are secreted by the cell in order to act outside it, though for the benefit of the organism. The latter include the well-known ferments that break down food substances in the digestive tract (digestion) and are released in the oral cavity (ptyalin), the stomach (pepsin, chymosin), and the intestine (trypsin, steapsin, amylopsin, etc.).
F. 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, and not tumultuously.
Enzymes are usually classified according to the reactions they catalyse; two large categories are thus distinguished: 1) hydrolases, or hydrolytic enzymes, which catalyse reactions that cause the breakdown of a complex molecule into simpler ones with the uptake of a water molecule, as in the cleavage of sucrose into glucose and fructose. 2) desmolases, or desmolytic enzymes, which serve to accelerate the breakdown of the simpler molecules resulting from hydrolysis, and the complete oxidation of organic substances to water and carbon dioxide. Particularly important in this category of enzymes are the oxidases and dehydrogenases, oxidising f.
The mechanism of action of f. consists in decreasing (or increasing) the chemical inertia of the fermented substrate by means not always fully known, but which generally lead to the formation of intermediate compounds between substrate and enzyme.
BIBLI: In addition FISIOLOGIA (v.), the following may be consulted: F. Haurowitz, Fortschritte der Biochemie (1938-1947), Basilea 1948. Vittorio Capraro