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Molecular Pharmacology, Vol 14, 665-671, Copyright © 1978 by the American Society for Pharmacology and Experimental Therapeutics

Inhibition of Azoreductase by Oxygen

The Role of the Azo Anion Free Radical Metabolite in the Reduction of Oxygen to Superoxide

RONALD P. MASON 1, FRANCIS J. PETERSON 1, and JORDAN L. HOLTZMAN 1

1 Veterans Administration Hospital, Minneapolis, Minnesota 55417, and Departments of Laboratory Medicine and Pathology, Medicinal Chemistry, Pharmacology, and Medicine, University of Minnesota, Minneapolis, Minnesota 55455

Microsomal azo reduction of the diazonaphthol dye sulfonazo III is strongly inhibited by oxygen. The sulfonazo III anion radical metabolite, which is apparently the first intermediate of azoreductase activity, appears to react with oxygen in aerobic microsomal incubations. Even though the sulfonazo III is unchanged in aerobic NADPH-supplemented microsomal incubations, oxygen consumption increases 10-fold to 122 nmoles/min/mg of protein. This stimulated oxygen consumption is partially reversed by either superoxide dismutase or catalase. Concomitant with the increase in oxygen uptake is a 9-fold increase in the rate of superoxide formation. The oxidation of NADPH is also greatly increased by sulfonazo III, but is not influenced by superoxide dismutase or catalase. These results suggest that futile formation of the sulfonazo III anion free radical mediates oxygen reduction to O2- and NADPH oxidation, and that NADPH is not being oxidized by a superoxide-NADPH chain reaction.

Submitted on December 28, 1977
Accepted on February 7, 1978






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