Biochemistry

In addition to these factors, the activity of enzymes is influenced by the presence in the solution of a number of chemical compounds that can activate (activators) or inhibit (inhibitors) the action of enzymes. Activators are represented by ions of many metals (most often Mg 2+ , Mn 2+ , K + , Co 2 ), some anions (СГ). So, amylase of saliva and pancreas are activated by chlorine anions; action of pancreatic juice lipase stimulate bile acids. Activators of many enzymes are metals. The mechanism of activation of enzymes by metal ions consists in the fact that in some cases they are part of the prosthetic group of enzymes and facilitate the formation of the enzyme-substrate complex, and in others they facilitate the attachment of the coenzyme to the apoenzyme or ensure the formation of the quaternary structure of the enzyme. Simple chemical compounds act as allosteric activators. Joining the allosteric center of the enzyme, they alter the tertiary structure of the protein molecule. As a result, the active and substrate-binding sites of the enzyme acquire the most favorable configuration for interaction with the substrate (Fig. 3.6). Some enzymes are produced in an inactive form in the form of proenzymes, or enzymes (precursors). Their active center is masked by an additional portion of the polypeptide chain, so the substrate cannot connect to it. Removal of such an additional site leads to the release of the active center and the possibility of the formation of an enzyme-substrate complex. So, the pepsin proenzyme - pepsinogen is activated by hydrochloric acid with cleavage of a small peptide chain. As a result, an active proteolytic enzyme is formed - pepsin. Inhibitor Figure 3.6 - Model of allosteritic enzymes Inhibitors inhibit the action of enzymes. There are two types of inhibition: irreversible and reversible. Irreversible inhibition is associated with the action of such substances that disrupt the entire structure of the enzyme, including the active center (for example, under the action of strong acids and bases, salts of heavy metals). 87