Reaction of Oxygen with Radiation-Induced Free Radicals on Single-Stranded Polynucleotides

Abstract

Pulse radiolysis experiments were carried out to investigate the reaction of O2 with the radicals produced by .cntdot.OH attack on nucleic acid derivatives and single-stranded polynucleotides. The .cntdot.OH adducts of the pyrimidine polynucleotides poly C and poly U reacted with O2, giving rise to species whose absorption spectra were similar to the peroxy adducts of the monomers CMP and UMP. There may be 2 forms of polynucleotide radicals, reacting with O2 at different rates. The situation for purine polynucleotides was complex. Radicals on single-stranded [calf thymus] DNA reacted with O2 on the same time scale as the reaction of O2 with .cntdot.OH adducts on pyrimidine polynucleotides. Typical values of the rate constant for this reaction are .apprx. 4 .times. 108 M-1 S-1, a value which agreed approximately with an estimated collision frequency of O2 with the polynucleotide radicals.