Cobalt(III) carboxypeptidase A: an activity depending on the method of metal ion replacement.

There are two different methods available for replacing the Zn(II) in carboxypeptidase A with Co(II). One involves direct metal ion exchange using a large molar excess of Co(II) while the other requires the preparation of the metal-free apoenzyme and reconstitution with Co(II). Oxidation of the product obtained by the first route gives Co(III) carboxypeptidase A which is inactive towards synthetic peptide substrates but active towards synthetic ester substrates. In contrast, oxidation of the Co(II) carboxypeptidase obtained by the second strategy gives a Co(III) carboxypeptidase A having neither peptidase nor esterase activity.