Selective binding behavior of zinc(II) and copper(II) ions to their native sites of apo-bovine superoxide dismutase.

The four binding constants of zinc(II) ions to apo-bovine superoxide dismutase were measured by the method of equilibrium dialysis. The binding constants (10(11.1)-10(10.9) M-1) of zinc ions to the native zinc sites were much larger than those to the native copper sites (10(7.8)-10(6.5) M-1) at pH 6.25. The competitive reaction between copper(II) and zinc(II) ions for the native copper sites of copper free bovine superoxide dismutase was also investigated. The native copper sites of bovine superoxide dismutase selectively react with copper ions, because the binding constants of copper ions for the native copper sites were much larger (10(6) times) than those of zinc ions.