Role of oxygen radicals in phenazine mediated ATP synthesis obtained with spinach chloroplasts: Toxicity of OH • radicals

Abstract

Superoxide anions and hydroxyl radicals are produced during the reduction of oxygen by reduced phenazine methosulphate or pyocyanine. Chloroplasts synthesize ATP when this reaction occurs. It is shown that orthophosphate, in the presence or absence of superoxide dismutase, increases the dismuta- tion of superoxide anions with a concomitant production of hydroxyl radicals. Superoxide dismutase was found to inhibit the ATP synthesis obtained with chloroplasts in darkness. In contrast, it is shown that superoxide dismutase with catalase, which inhibit the production of hydroxyl radicals, enhance ATP synthesis. Similarly the presence of methional, a scavenger of hydroxyl radicals, increases ATP synthesis. The possible participation of the superoxide anion in orthophosphate dehydroxylation, and the inhibitory action of the hydroxyl radical on phosphorylation, are discussed.