Measurement of apparent binding constant between copper ion and apo-bovine superoxide dismutase

Abstract

The binding constants of copper ions to apo-bovine superoxide dismutase were measured by the method of equilibrium dialysis. The binding constant (10 8.9 M −1) of copper ion to the native copper site was much larger (10 6 times) than that to the native zinc site at pH 4.0. The two native binding sites of copper ions are identical and show no interaction in the measurement of the binding constants. The binding of copper ions to the native zinc sites involved release of two protons and competition between these two protons and copper ion was governed by the pH dependence of copper binding constant to the native zinc sites.