[Mechanism of action of cAMP-dependent protein kinase. III. Probable role of an enzyme carboxyl group].

By the method of chemical modification the active site of cAMP-dependent pig brain protein kinase was shown to contain a carboxyl group. The kinetic parameters of irreversible inhibition of the enzyme by water-soluble carbodiimide in the presence of ethyl ester of glycine were determined. The ionized carboxyl group-containing amino acid residue found is evidently localized in the immediate proximity to the reaction center. The comparison of the reaction rates of phosphate transfer from the intermediate phosphoform of the enzyme under native and denatured conditions suggests that this residue acts as the general base catalyst of this process.