HYDRATED ELECTRON-INITIATED MAIN-CHAIN SCISSION IN PEPTIDES - ESR AND SPIN-TRAPPING STUDY

The reactions of hydrated electrons (eaq-) with 19 tripeptides were investigated. Hydrated electrons were produced by γradiolysis of aqueous peptide solutions containing sufficient sodium formate to remove hydroxyl radicals and hydrogen atoms. t-Butanol was also used to scavenge hydroxyl radicals. The short-lived radicals formed by the reactions of eaq- with the peptides were spin-trapped with t-nitrosobutane to form stable nitroxide radicals and identified by e.s.r. spectroscopy. The tripeptides studied contained two glycine residues. Following the addition of eaq- to tripeptides, C-N bond scission was observed at three sites. Cleavage occurred between the nitrogen of the ammonium group and the αcarbon and between the nitrogen of the peptide linkage and the adjoining αcarbons. The radicals corresponding to each of these three types of scission were identified. From a comparison of the radical yields of the reaction of eaq- with ala, (ala)2, (ala)3 and poly-DL-alanine, with an average degree of polymerization of 1800, it was shown that eaq- can react with many carbonyl groups of poly-DL-alanine, leading to main-chain scission. Analogous reactions of eaq- with proteins and enzymes may be expected to lead to loss of biological activity. © 1978 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.