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The optical properties, copper content, catalytic activity and quaternary structure of many preparations of ascorbate oxidase purified with two different methods were examined.

Summary The enzymatic destruction of oxidizing products produced during metabolic reduction of oxygen in the cell (such as singlet oxygen, H2O2 and OH radical) involves the concerted action of superoxide dismutase-which removes O2- and yields H2O2-and H2O2 removing enzymes such as catalase and glutathione peroxidase. A difference in distribution or ratio of these enzymes in various tissues may result in a different reactivity of oxygen radicals.

Summary (1)45% of the total copper of green zucchini ascorbate oxidase is EPR-detectable. At least two species of copper are present, one with a small A? (Type 1) and one with a large A? (Type 2). Computer simulated spectra indicated 50% contribution by each type of copper.(2)Azide inhibited ascorbate oxidase activity by an uncompetitive mechanism. EPR and optical spectra performed on titration of ascorbate oxidase with azide indicated the formation of a copper-azide complex. The Type 2 copper appears to be the binding site of azide. The involvement of the EPR non-detectable copper as an anion binding site with high affinity toward azide can not be excluded.