Production of O2 in Photolyzed Water Demonstrated Through the Use of Superoxide Dismutase*

Abstract— The photolysis of water has been studied using ferricytochrome c as the detector of reducing radicals and ferrocytochrome c as the detector of oxidizing radicals. Mannitol was used as a scavenger of hydroxyl radicals and superoxide dismutase was used to expose the specific involvement of superoxide radicals. Aerobic photolysis caused a reduction of ferricytochrome c , which was inhibited by superoxide dismutase and was enhanced by mannitol. Aerobic photolysis also caused the oxidation of ferrocytochrome c , which was inhibited by mannitol and augmented by superoxide dismutase. The presence of superoxide dismutase also eliminated the effects of mannitol on the aerobic oxidation of ferrocytochrome c. Photolysis in the absence of oxygen also caused the reduction of ferricytochrome c and the oxidation of ferrocytochrome c , but under these anaerobic conditions neither mannitol nor superoxide dismutase exerted significant effects. An explanation of these observations is offered in terms of the reactivities of H . , OH . and O ‐ 2 radicals.