Hydrogen Transfer from Exchangeable to Carbon-Bound Sites in γ-Irradiated Dry Proteins

γ-Radiolysis in vacuo of dry ribonuclease and poly-DL-alanine, in which 40-60% of the exchangeable sites have been tritium-labeled, leads to the transfer of hydrogen from exchangeable to carbon-bound sites. Tritium incorporation is a linear function of dose from 5 to 30 Mrads. The G values for hydrogen transfer at 298°K are 3.0 for ribonuclease and 2.1 for poly-DL-alanine. The G values for ribonuclease at 195°K and 77°K are 0.7 and ≦0.1, respectively. There are many similarities between the distribution of tritium among the amino acids obtained by γ-irradiation-induced hydrogen transfer and that produced by the addition of tritiated radical scavengers to previously γ-irradiated proteins. The latter is a measure of the secondary radicals produced at 298°K. Experiments with tritiated ammonia indicate that hydrogen transfer cannot be induced by secondary radicals after γ-radiolysis. For ribonuclease at 298°K, hydrogen is transferred with a G value which is approximately equal to the total initial radical yie...