PHOTOINDUCED GENERATION OF HYDROGEN PEROXIDE AND HYDROXYL RADICALS IN MELANINS

The hydrogen peroxide produced during photolysis of melanin pigments has been measured using an oxidase electrode. The photooxidation has been shown to occur via the superoxide intermediate. In the presence of superoxide dismutase the rate of photo‐induced production of hydrogen peroxide is increased, reflecting the ability of melanin to scavenge superoxide radicals. Evidence for metal‐ion dependent formation of hydroxyl radicals during photooxidation of melanin pigments was obtained using electron spin resonance‐spin trapping procedures. Superoxide dismutase increased the rate of formation of hydroxyl radicals in the system. Mechanisms of metal ion‐induced production of hydroxyl radicals during photolysis of melanin pigments are discussed.