ESR AND SPIN-TRAPPING STUDIES OF REACTIONS OF HYDRATED ELECTRONS WITH DIPEPTIDES

The reactions of hydrated electrons (eaq-) 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 eaq-, 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 eaq- 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 βalanine as the amino terminal residue and for acetyl and formyl amino acids. The secondary deamination reactions of eaq- 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. © 1978 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.