Effects of Gamma Radiation on Ribonuclease

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Abstract
Irradiated in the solid state, ribonuclease is resistant to chemical covalent changes such as splitting of disulfide bonds or destruction of methionine, tyro-sine, or phenylalanine even up to 45 Mr. Enzymatic activity declines markedly, however, and at a rate similar to the decrease of "hard-to-exchange amide hydrogens." When ribonuclease is irradiated in solution, the rate of destruction of the amino acids and that of the lowering of % "hard-to-exchange amide hydrogens" are of similar magnitude. In terms of fraction of total amino acids rather than absolute number of molecules affected, smaller amounts of gamma-radiation are necessary to elicit equal changes for the ribonuclease irradiated in solution.