PHOTODYNAMIC GENERATION OF HYDROXYL RADICALS BY HEMATOPORPHYRIN DERIVATIVE AND LIGHT

Abstract

Abstract In a reaction mixture containing hematoporphyrin derivative, deoxyribose, Fe 3+ ‐EDTA and either methionine or tryptophan, hydroxyl radicals were formed during illumination with visible light. When either hematoporphyrin derivative, Fe 3+ ‐EDTA or the amino acid was omitted from the reaction mixture, the generation of hydroxyl radicals ceased. These observations suggest an iron‐catalyzed Haber‐Weiss reaction, involving superoxide and hydrogen peroxide in the generation of hydroxyl radicals. It could be shown that with methionine H 2 O 2 was indeed an essential intermediate in the reaction sequence. With tryptophan, however, H 2 O 2 , was not generated. Apparently a photooxidation product of tryptophan could replace H 2 O 2 in the OH‐generating reaction with Fe 2+ ‐EDTA. Although superoxide was generated in the reaction mixture, it was not an indispensable intermediate. Apparently a porphyrin radical, formed via photoexcitation of hematoporphyrin derivative, could replace superoxide in the Haber‐Weiss reaction.