Structural changes in metalloenzyme in the course of metal substitution: carboxypeptidase B

Native and zinc reconstituted carboxypeptidase B were nitrated with tetranitromethane. The inactivation of the reconstituted enzyme was faster than that of the native enzyme and was accompanied by the formation of a considerable amount of enzyme dimers. The inactivation and dimerization reflected changes in the reactivity of active site tyrosine residue(s), thus indicating microenvironmental changes which occur during metal substitution. The change in tyrosine reactivity could be correlated with the residence of the enzyme in the metal-free state.