Role of intermolecular reactions in the formation of secondary radicals in proteins irradiated in the dry state.

Abstract

The mechanism of formation of secondary radicals in x-irradiated proteins has been studied by electron spin resonance spectroscopy. Ribonuclease, thiolated gelatin, and egg albumin were irradiated at 77°K, alone, as well as in the presence of oxygen or adenine. The spectra were recorded immediately after irradiation and after heat-treatment to predetermined temperatures. The presence of high concentrations of adenine during irradiation prevented the formation of sulfur radicals in ribonuclease and doublet-type radicals in thiolated gelatin. The presence of oxygen did not alter the radical yield or the qualitative spectra observed at 77°K. Oxygen, like adenine, prevented the formation of the typical secondary radicals on heat-treatment. Qualitative spectra were observed which were ascribed to transient HO2 radicals, presumed to be formed by decomposition of organic peroxide radicals. The results are interpreted to mean that in proteins irradiated in vacuum the secondary radicals formed on heat-treatment ar...