Hydrated Electron-initiated Main-chain Scission in Peptides

Summary

The reactions of hydrated electrons (e_aq⁻) with 19 tripeptides were investigated. Hydrated electrons were produced by γ-radiolysis 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 e_aq⁻ 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 e_aq⁻ to tripeptides, C-N bond scission was observed at three sites. Cleavage occurred between the nitrogen of the ammonium group and the α-carbon and between the nitrogen of the peptide linkage and the adjoining α-carbons. The radicals corresponding to each of these three types of scission were identified. From a comparison of the radical yields of the reaction of e_aq⁻ with ala, (ala)₂, (ala)₃ and poly-DL-alanine, with an average degree of polymerization of 1800, it was shown that e_aq⁻ can react with many carbonyl groups of poly-DL-alanine, leading to main-chain scission. Analogous reactions of e_aq⁻ with proteins and enzymes may be expected to lead to loss of biological activity.