Conformational Properties of Enzymes and Ionization

Abstract

An enzyme macromolecule contains ionizable groups — cationic and anionic amino acid residues. Ionizable groups may also be present in coenzymes, substrates, inhibitors, and activators, i.e., in any effector. Enzymatic activity thus depends to a large extent on medium pH and hence on the degree of ionization of the corresponding groups. Inhibition and activation of an enzyme also depend on pH. The aforementioned bell-shaped curve dependence on pH is usually observed for enzymatic activity (see p. 87): activity is maximal at some intermediate pH characteristic of the enzyme in question and decreases at larger or smaller pH’s, although it does not reach the values corresponding to alkaline and acidic denaturation of the protein.