Metal Ion Binding and Activation of Streptomyces griseus Dinuclear Aminopeptidase
—Cadmium(II) Binding as a Model

Catrin Hasselgren,^# Hyun Ik Park, and Li-June Ming*

Department of Chemistry and
Institute for Biomolecular Science
University of South Florida
Tampa, Florida 33620-5250

^# Current address:
Department of Inorganic Chemistry
Chalmers University of Technology
S-412 96 Göteborg, Sweden

Abstract

The metal binding and activation of the dinuclear aminopeptidase from Streptomyces griseus has been studied by means of metal titration, kinetics, and thermodynamics using Cd²⁺ as a probe.  Cd²⁺ binds to the two metal-binding sites in a sequential manner to produce a highly active Cd²⁺-substituted derivative, particularly in the presence of Ca²⁺.  The first stepwise affinity constant for the binding of metal to the dinuclear metal-binding site was found to determine the selectivity, regardless of the second stepwise affinity constant.  Although the selectivity of Cd²⁺ binding to this enzyme is not as great as Co²⁺, it is nevertheless similar to Zn²⁺ binding.  Moreover, Ca²⁺ was found to significantly affect the metal binding and activation, inhibition, and entropy of activation of this enzyme.

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