Summary
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.