Enzymes (enzymes) are high molecular weight organic compounds of a protein nature that play the role of biological catalysts in the body .
The mechanism of action of enzymes
Elucidation of the mechanisms underlying the catalytic action of enzymes is one of the fundamental problems and urgent problems of not only enzymology, but also modern molecular biochemistry and biology.
Long before pure enzymes became available and their nature was clarified, there was a belief that the combination of the enzyme with the substrate was crucial for the implementation of the enzymatic process. Attempts to detect a complex compound of the enzyme with the substrate for a long time did not lead to success, since such a complex is labile, it decomposes very quickly. Using the spectroscopy method made it possible to identify enzyme-substrate complexes for catalase, peroxidase, alcohol dehydrogenase, and flavin-dependent enzymes.
The method of X-ray diffraction analysis made it possible to obtain a lot of important information about the structure and catalytic mechanisms of the action of enzymes. This method was used to establish the connection of substrate analogues with lysozyme and chymotrypsin enzymes.
Some direct evidence of the existence of enzyme-substrate complexes has been obtained for cases when, at one stage of the catalytic cycle, the enzyme is bound to the substrate by a covalent bond. An example is the hydrolysis reaction of n-nitrophenyl acetate catalyzed by chymotrypsin. When the enzyme is mixed with this ester, chymotrypsin is acetylated at the hydroxyl group of the reactive serine residue. This stage is fast, but the hydrolysis of acetylchymotrypsin with the formation of acetate and free chymotrypsin is much slower. Therefore, in the presence of n-nitrophenyl acetate, acetylchymotrypsin accumulates, which is easy to detect.
The presence of a substrate in the enzyme can be "captured" by converting the unstable EC complex to an inactive form, for example, by treating the enzyme-substrate complex with sodium borohydride, which has a strong reducing effect. A similar complex in the form of a stable covalent derivative was found in the aldolase enzyme. It turned out that the e-amino group of lysine interacts with the substrate molecule.
The substrate interacts with the enzyme in a certain part, which is called the active center, or the active zone of the enzyme.
The active center, or active zone, is understood to mean that part of the enzyme protein molecule that binds to the substrate (and cofactors) and determines the enzymatic properties of the molecule. The active center determines the specificity and catalytic activity of the enzyme and should be a structure of a certain degree of complexity, adapted for close approximation and interaction with the substrate molecule or its parts directly involved in the reaction.
Among the functional groups, they are distinguished between those that are part of the “catalytically active” site of the enzyme and form the site that provides a specific affinity (binding of the substrate to the enzyme) - the so-called contact, or “anchor” (or adsorption site of the active center of the enzyme).
The mechanism of action of enzymes explains the Michaelis-Menten theory. According to this theory, the process takes place in four stages.
The mechanism of action of enzymes: stage I
Between the substrate (C) and the enzyme (E), a bond arises - an enzyme-substrate EC complex is formed in which the components are linked together by covalent, ionic, aqueous and other bonds.
The mechanism of action of enzymes: stage II
Under the influence of the attached enzyme, the substrate is activated and becomes available for the corresponding EC catalysis reactions.
The mechanism of action of enzymes: stage IIII
The catalysis of the EU is taking place. This theory is confirmed by experimental studies.
And finally, stage IV is characterized by the release of the enzyme E molecule and reaction products P. The sequence of transformations can be represented as follows: E + C - EC - EC * - E + P.
The specificity of the action of enzymes
Each enzyme acts on a specific substrate or group of substances that are similar in structure. The specificity of the action of enzymes is explained by the similarity of the configuration of the active center and the substrate. In the process of interaction, an enzyme-substrate complex is formed.