COMPARATIVE STUDY OF OXIDATION OF NUCLEIC ACID COMPONENTS BY HYDROXYL RADICALS, SINGLET OXYGEN AND SUPEROXIDE ANION RADICALS

Abstract— Superoxide radicals, singlet oxygen and hydroxyl radicals are individually or in combination involved in radiation or photochemical processes and in various enzymatic reactions. The reactivity and the mechanism of reaction of these oxygen species with some biologically significant DNA components were investigated through the characterization of the final oxidation products.
Superoxide radicals appear to be unreactive with purine and pyrimidine 2'-deoxyribonucleosides. However, the autoxidation reaction of 6-hydroxydopamine leads to extensive degradation of thymine through the intermediary of hydroxyl radicals. Chemically and microwave-discharge generated singlet oxygen oxidation is specific to 2'-deoxyguanosine. The main oxidized products of these reactions were also characterized as well as an as yet unidentified nucleoside in the methylene-blue photooxydation of 2-deoxyguanosine. These results, in addition to specific deuterium effect experiments, lend support to the involvment of singlet oxygen (type II mechanism) in the methylene-blue photosentization. No singlet oxygen effect was observed in aqueous irradiated system.