Porcine carboxypepticase B: Multiple substrates binding modes

The kinetics of porcine carboxypeptidase B catalyzed hydrolysis of hippurylarginine, hippurylargininic acid, Z·Ala₃ and hippurylphenyllactic acid have been examined in order to elucidate the substrate specificity of the enzyme. Activity toward both basic and non-basic (i.e., hydrophobic type) substrates has been confirmed. However, it would appear that these substrates are not all bound in the same manner to the same site. The pH dependencies of the kinetic parameters revealed characteristic differences among the two types of substrates. Furthermore, inhibition studies with L-argininic acid, e{open}-aminocaproic acid, Z-D-Ala-L-Arg and β-phenylpropionic acid support this postulate. These studies provide insite regarding possible pathways for the evolution of the carboxypeptidases.