Kinetic studies of modifier effects on the carboxypeptidase A catalyzed hydrolyses of peptides

A variety of modifiers of carboxypeptidase A (CPA) have been investigated in an effort to understand the structural requirements of inhibitors and activators of peptidase activity. It is proposed that an understanding of the mechanism of action of reversible activators of the enzyme may bear on the long standing question of whether the detailed mechanism of peptidase activity is different from that of esterase activity. An analog of the activator 2,2-dimethyl-2-silapentane-5-sulfonate, 5,5-dimethylhexanoate, was found to be a competitive inhibitor of the CPA-catalyzed hydrolysis of benzoylglycyl-L-phenylalanine. The modifier 4-phenyl-3-butenoate (styrylacetic acid) was determined to be an activator. The sulfonates benzene-sulfonate, p-toluenesulfonate, phenylmethanesulfonate, 2-phenylethanesulfonate, and 3-phenylpropanesulfonate were all found to be activators.