Mechanism of action of enzymes

Enzymes (enzymes) are high-molecular organic compounds of protein nature that perform in the body the role of biological catalysts.

The elucidation of the mechanisms underlyingcatalytic action of enzymes, is one of the fundamental tasks and urgent problems not only of enzymology, but also of modern molecular biochemistry and biology.

Long before the netenzymes and their nature was clarified, there was a conviction that the combination of the enzyme with the substrate is crucial for 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 decays very rapidly. Using the method of spectroscopy made it possible to identify enzyme-substrate complexes for catalase, peroxidase, alcohol dehydrogenase, flavin-dependent enzymes.

The X-ray diffraction method allowedget a lot of important information about the structure and catalytic mechanisms of enzyme action. This method was used to establish the connection of analogues of the substrate with enzymes lysozyme and chymotrypsin.

Some direct evidence of existenceEnzyme-substrate complexes were obtained for cases when at one stage of the catalytic cycle the enzyme is bound to the substrate by a covalent bond. As an example, the hydrolysis of n-nitrophenyl acetate catalyzed by chymotrypsin can serve. When the enzyme is mixed with this ether, chymotrypsin is acetylated at the hydroxyl group of the reactive serine residue. This stage proceeds rapidly, however, the hydrolysis of acetylchymotropin with formation of acetate and free chymotrypsin is much slower. Therefore, in the presence of n-nitrophenyl acetate, acetylchymotrypsin is accumulated, which is easy to detect.

The presence of a substrate in the enzyme can be"Catch" by transferring the unstable EC complex to an inactive form, for example by treating the enzyme-substrate complex with sodium borohydride, which has a strong reducing action. A similar complex in the form of a stable covalent derivative was found in the enzyme aldolase. 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.

Under the active center, or active zone,understand that part of the enzyme protein molecule that connects 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 approach and interaction with the substrate molecule or its parts directly involved in the reaction.

Among the functional groups, there arecomposition of the "catalytically active" region of the enzyme and forming a 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 occurs in four stages.

Mechanism of action of enzymes: Stage I

Between the substrate (C) and the enzyme (E), a bond arises - an enzyme-substrate complex of the EC is formed, in which the components are linked together by covalent, ionic, aqueous and other bonds.

Mechanism of action of enzymes: Stage I

The substrate under the action of the attached enzyme is activated and becomes available for the corresponding catalysis reactions of the EU.

Mechanism of action of enzymes: IІI stage

The catalysis of the EU is being carried out. This theory is confirmed by experimental studies.

Finally, stage IV is characterized by the release of the enzyme molecule E and the products of the reaction P. The sequence of transformations can be expressed as: E + C - EC - EC * - E + P.

Specificity of action of enzymes

Each enzyme acts on a specific substrateor a 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.