Concerted Action Of Reduced Glutathione And Superoxide Dismutase In Preventing Redox Cycling Of Dihydroxypyrimidines, And Their Role In Antioxidant Defence

Dialuric Acid, the reduced form of the β-cell toxin alloxan, and the related fava bean derivatives divicine and isouramil, autoxidize rapidly in neutral solution by a radical mechanism. GSH promotes redox cycling of each compound, with concomitant GSH oxidation and H₂O₂ production. With superoxide dismutase present, there is a lag period in which little oxidation occurs, followed by rapid oxidation. GSH extends this lag and decreases the subsequent rate of oxidation, so that with superoxide dismutase and a sufficient excess of GSH. coupled oxidation of GSH and each pyrimidine is almost completely suppressed. This mechanism may be a means whereby GSH in combination with superoxide dismutase protects against the cytotoxic effects of these reactive pyrimidines. Superoxide dismutase may also protect cells against oxida-tive stress in other situations where GSH acts as a radical scavenger. and we propose that the concerted action of GSH and superoxide dismutase constitutes an important antioxidant defence