Molecular results and considerations related to the biological effects of near-uv

Near-uv photooxidation of tryptophan generates N-formylkynurenine, an acylformanilide (AF) which can promote near-uv photooxidation of various biomolecules, and hydrogen peroxide. Experiments employing superoxide dismutase have demonstrated the involvement of superoxide in such photooxidations. Nucleosides and their 5'-monophosphate esters in aqueous solution are subject to near-uv AF promoted photooxidation with concomitant hydrogen peroxide formation. The decreasing order of susceptibility to this photooxidation was found to be: guanosine, adenosine, thymidine, uridine, cytosine. Amount of photooxidation was greatest under acidic (pH 2) conditions and least in neutral media. AF promoted photooxidation of thymidine proceeds selectively at the methyl group to afford as ultimate products 5-hydroper-oxymethyl-, 5-hydroxymethyl-, and 5-hydroxy-2'-deoxyuridine. Experiments seeking explanation for the observed synergistic lethality to bacteriophage by simultaneous action of near-uv and hydrogen peroxide have uncovered the formation of a near-uv (305 nm) chromophore by treatment of peptide cysteine with hydrogen peroxide