Metallocarboxypeptidases: A cadmium - Carboxypeptidase B with peptidase activity

The replacement of zinc by a series of other metal ions (Co, Cd, Mn) resulted in enzymatically active carboxypeptidases both as peptidases and esterases. The effect of the metal replacement on the kinetic parameters varies for the various substrates. Cd-CPB, previously known for its lack of peptidase activity, shows enhenced activity as long as the substrate interact with four subsites (including the N-terminal blocking group). Kinetic measurements and chemical modification revealed differences in the nature of the residues necessary for the proper alignment along the active site between the Zn and Cd carboxypeptidases. A simple explanation of the data observed is based on the assumption that replacement of the metal affects the microenvironment of the active site.