Radical Distributions in γ-Irradiated Dry Proteins at 195°K

Gamma radiolysis of dry proteins at 195°K in the presence of tritiated hydrogen sulfide gives information about the distribution of carbon radicals which are precursors of the secondary radicals observed at 298°K. When lyophilized ribonuclease, lysozyme, chymotrypsinogen, and nagarse (a protein without disulfide bridges) are irradiated at 195°K, the observed tritium distributions are approximately equivalent; however, at 298°K characteristic distributions are found. Thus, the mechanisms for the formation of carbon radicals in native proteins can be divided into two groups: first, those which take place below 195°K and are independent of amino acid sequence, conformation, and the presence of disulfide bridges; and second, those which occur above 195°K and are influenced by the specific conformation of each native protein.