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.

Mechanism of action of enzymes

The elucidation of the mechanisms underlying the catalytic 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 pure enzymes became available and their nature was clarified, the conviction was formed that the connection of the enzyme with the substrate is 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 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 method of X-ray diffraction analysis made it possible to obtain many important data on the structure and catalytic mechanisms of the action of enzymes. This method was used to establish the connection of analogues of the substrate with enzymes lysozyme and chymotrypsin.

Some direct evidence for the existence of enzyme-substrate complexes was 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 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 "captured" by transferring an 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, is meant 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, the part of the "catalytically active" part of the enzyme is distinguished 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 is formed - 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

EC catalysis is being carried out. This theory is confirmed by experimental studies.

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

Specificity of 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. During the interaction, an enzyme-substrate complex is formed.