Studies on the aerobic photooxidation of cysteine using riboflavin as a sensitizer: evidence for the photogeneration of a superoxide anion and hydrogen peroxide.

The riboflavin sensitized oxidation of cysteine under an aerobic condition was investigated. The effects of various scavengers, such as superoxide dismutase, catalase, mannitol, sodium azide and potassium ferrocyanide (an electron donor), on the photooxidation were determined. A reaction mechanism involving the superoxide anion is proposed for the photooxidation of cysteine to cysteic acid.