[Hydrogen-adduct radicals in thymidine and thymidine 5'-monophosphate photosensitized by proflavin. Protection by sulfur compounds (author's transl)].

At pH values 5 and 9, the influence of cysteine, cystine, 3-mercaptopropionic acid and S-methylcysteine on the induction of H-adduct radicals in thymidine and thymidine 5'-monophosphate photosensitized by proflavin is investigated. The results obtained indicate that efficient protection is given when the electrostatic interactions between the charged groups of the molecules present allow the close proximity of a thiol or a disulfide bridge and the proflavin - DNAs complex constituent. The scheme proposed for the mechanism involves the capture by the protector of an electron or a proton, indispensable intermediates in the formation of the H-adduct radicals.