Studies on the Gamma Ray Irradiation on the Protein

Abstract

Co/sup 60/ irradiation of proteins was carried out at a rate of 3000 r/ min in vacuo or in an atmosphere of oxygen or nitrogen. The electron spin resonance (ESR) absorption spectra of irradiated bovine and human serum albumin, fibrin, and silk fibroin were determined. It was shown that the free radicals in the irradiated proteins are associated with their cystine or cysteine content. The higher the content of these sulfur-containing amino acids in irradiated proteins, the more their ESR patterns resemble those of cystine and cysteine. Irradiated silk fiber provided a doublet similar to that of glycyl-glycyl-glycine. Such an orientation-dependent pattern could be explained as an unpaired electron localized on the oxygen atom hydrogenbonded to the NH group of the adjacent polypeptide chain. When irradiation was done in the presence of oxygen, the ESR signals of proteins were markedly different from those irradiated in vacuo, the former being attributable to peroxide radicals. Proteins irradiated in the presence of water barely provided a detectable ESR signal. When irradiated albuim or cysteine were dissolved into the solution of native albumin, the titrable SH group decreased, probably due to reaction of sulfhydryl radicals with the SH group. It is concluded that themore » effect of radiation on protein solutions is chiefly, if not entirely, attributable to radicals from the irradiated water, and that the decrease in the SH group of irradiated protein solution can be partly ascribed to free radical reactions. (H.H.D.)« less