E.S.R. and Spin-trapping Studies of the Reactions of Hydrated Electrons with Dipeptides

Summary

The reactions of hydrated electrons (e_aq⁻) with 55 dipeptides and 25 acetyl and formyl amino acids have been studied by e.s.r. and spin-trapping techniques. Gamma-radiolysis of deaerated aqueous solutions was used to generate e_aq⁻, and sodium formate or t-BuOH was added to scavenge the OH radicals. t-Nitrosobutane was employed as the spin-trapping reagent. The radical, -ĊO⁻-NH-, which is the initial product of the reactions of e_aq⁻ with dipeptides, was observed only for val-gly, val-ala, val-leu and ile-ala. For most of the dipeptides this radical converts to the primary deamination radical, ĊHR′-CONH-CHR-COO⁻, where R and R′ are the side-chains of the common amino acids. In many cases a radical of the type ĊHR-COO⁻, formed by secondary deamination, was also observed. Only secondary deamination reactions were observed for dipeptides containing β-alanine as the amino terminal residue and for acetyl and formyl amino acids. The secondary deamination reactions of e_aq⁻ with dipeptides, acetyl and formyl amino acids in aqueous solutions have not been observed previously. This type of reaction is of interest since it brings about main-chain scission in polypeptides and proteins.