On the interaction of esters and peptides with carboxypeptidase B.

The specificity of porcine carboxypeptidase B towards basic and non-basic substrates was studied by employing several esters of phenyllactate. The structure of these depsipeptides complement exactly those of the corresponding phenylalanyl oligopeptide substrates. These non-basic ester-peptide pairs as well as the basic ester-peptide pair of arginyl derivatives, permits the direct comparison of the pH dependencies of the kinetic constants for the hydrolysis of those substrates by carboxypeptidase B. The data is interpreted in terms of three specific ionizing groups located at the active site of the enzyme. The mode and extent of inhibition of the hydrolysis of a specific substrate by another substrate was characterized kinetically. These results are discussed in relation to a proposed model for esterolytic and proteolytic action of carboxypeptidase B.