The effect of sulphur compounds on free radical reactions and formation in irradiated dry proteins

Abstract

The free radical reactions occurring in gamma-irradiated proteins: salmine, gelatin and zein, freeze-dried with mercaptoethylamine (cysteaine), cysteine or cystamine have been studied using electron spin resonance spectroscopy. It was found that at 77° K the energy was not absorbed randomly over the whole macromolecule and particularly an unpaired electron (probably an ion) was stabilised on a sulphur atom in the additive molecule. At room temperature the protein radicals migrated to the additive to give the radical, CH₂---S^·. This radical then reacted with a glycine residue according to the reaction: -CH₂-S^·+-CO-CH₂-NH-→ CH₂-SH+-CO-C^·H-NH- so that the major effect of the added sulphur compounds was to accelerate the rate of migration of the initial protein radicals to a glycine residue. Also they accelerated the decay of total radicals in proteins.