Effect of Irradiation on Some Lyophilized Proteins

Exposure of lyophilized native ribonuclease or lysozyme in vacuo to about 30 Mrads causes aggregation of the protein molecules. There is no evidence of extensive degradation of these globular molecules. Guanidine-HCl (4 M) does not disassemble the aggregated material. If the S-carboxymethylated form of ribonuclease or lysozyme (that is, a form devoid of disulfide linkages) is exposed to the gamma ray, there is also no indication of marked degradation of the polypeptide chain, and again the molecules are prone to aggregate. On the other hand, lathyritic collagen exhibits a definite lowering of molecular weight, under the same conditions. Equivalent irradiation in an hydrogen sulfide atomosphere rather than in vacuo causes a diminished aggregation of the S-carboxymethylated ribonuclease and less degradation of the collagen.