Aqueous radiation chemistry of protein and nucleic acid constituents: ESR and spin-trapping studies

Abstract

Our recent studies of the reactions of hydroxyl radicals, hydrated electrons and S̊O 4 − radicals with amides, amino acids, peptides, DNA constituents and related compounds are reviewed. Hydroxyl and S̊O 4 − radicals were produced by the photolysis of aqueous solutions of hydrogen peroxide and sodium peroxydisulfate, respectively. Hydrated electrons were generated by γ- radiolysis of deaerated aqueous solutions in the presence of sodium formate or t-butanol. The short-lived organic radicals were spin-trapped with t-nitrosobutane to form long-lived nitroxide radicals which could be identified by ESR. A new reaction of hydrated electrons with dipeptides and polypeptides was observed. In addition to the well-known reductive deamination of the N-terminal residue, scission between the nitrogen of the peptide bond and the alpha carbon also occurred. The advantages and limitations of spin-trapping compared to other methods of studying free radicals in aqueous solutions and future possibilities for the identification of radicals in γ-irradiated solutions of proteins and nucleic acids and in the corresponding solids by a combination of spin-trapping and chromatography are pointed out.