O2>-DEPENDENT and -INDEPENDENT PHOTOOXIDATION OF QUERCETIN IN THE PRESENCE and ABSENCE OF RIBOFLAVIN and EFFECTS OF ASCORBATE ON THE PHOTOOXIDATION

Abstract— The self-sensitized photooxidation of quercetin was not suppressed by superoxide dismutase (SOD), but suppressed by ascorbate. During the suppression of quercetin photooxidation, ascorbate was oxidized. These results suggest the reduction of oxidized quercetin to quercetin by ascorbate. Quercetin photooxidation in the presence of both riboflavin and EDTA was suppressed by SOD by about 90%. The result suggests the participation of O₂^- in the photooxidation of quercetin. The participation of O₂^- in the quercetin oxidation was confirmed by a xanthine-xanthine oxidase system. Based on these results the physiological and pharmacological functions of quercetin are discussed.