Superoxide Dismutase

Abstract

An enzyme which catalyzes the dismutation of superoxide radicals (O2·- + O2·- + 2H+ → O2 + H2O2) has been purified by a simple procedure from bovine erythrocytes. This enzyme, called superoxide dismutase, contains 2 eq of copper per mole of enzyme. The copper may be reversibly removed, and it is required for activity. Superoxide dismutase has been shown to be identical with the previously described copper-containing erythrocuprein (human) and hemocuprein (bovine). Stable solutions of the superoxide radical were generated by the electrolytic reduction of O2 in an aprotic solvent, dimethylformamide. Slow infusion of such solutions into buffered aqueous media permitted the demonstration that O2·- can reduce ferricytochrome c and tetranitromethane, and that superoxide dismutase, by competing for the superoxide radicals, can markedly inhibit these reactions. Superoxide dismutase was used to show that the oxidation of epinephrine to adrenochrome by milk xanthine oxidase is mediated by the superoxide radical. An assay of several tissues indicates that superoxide dismutase is widely distributed within mammalian organisms.