19F relaxation as a probe of the oxidation state of Cu, Zn superoxide dismutase. Studies of the enzyme in steady-state turnover

19F nmr relaxation proved to be a proper method to evaluate the Cu2+/Cu+ ratio at the active site of Cu, Zn superoxide dismutase in either equilibrium or turnover conditions. In the steady-state under fluxes of O2-, the enzyme was found to contain 50% Cu2+, in accord with the equal rates of copper catalytic reduction and oxidation. Previous results giving 75% Cu at the steady-state without change of the overall catalytic constant were confirmed for samples subjected to freeze-drying or freezing-thawing. © 1981 Academic Press, Inc.