The effect of metal ions on free radical formation and reactions in irradiated proteins

Abstract

The effect of different metal ions on free radical formation and reactions in gamma-irradiated bovine serum albumin and trypsin in the solid state has been studied using electron spin resonance spectroscopy. The metal ions lowered the radical concentration as observed at 77°k, and markedly reduced the concentration of -CH₂-S· radicals formed at room temperature. The results have been interpreted in terms of the reaction of radiation-produced electrons with the metal ions, and they confirm the postulate that, at 77°k, electrons are trapped on cystine residues in proteins and that the resultant cystine anion reacts at higher temperatures to give the -CH₂-S· radical. The E.S.R. results have been correlated with the results of Butler and Robins, who found that metal ions protected trypsin against high-energy radiation.