L-Cysteine-D-penicillamine mixed disulfide (CySSPen) was irradiated in aerated and deaerated aqueous solutions with 60Co γ-rays. G values were determined for all products identified after exposure to 10 000 rads. The major products were the sulfinic and sulfonic acids (CySO2H, CySO3H, and PenSO2H), the sulfhydryl derivatives (CySH and PenSH), symmetrical disulfides (CySSCy and PenSSPen), three trisulfides (CySSSCy, CySSSPen, and PenSSSPen), and ammonia. Each half of the disulfide behaved in exactly the same way as the corresponding symmetrical disulfide. Products from the CyS— part of the disulfide were dose rate dependent while products from the PenS— part were independent of dose rate. The reactions proposed for the symmetrical disulfides were adequate to explain radiolysis of the unsymmetrical disulfide.Radiolysis of a mixture of cystine and penicillamine disulfide was examined for comparison with the unsymmetrical disulfide and was found to give very similar results. It was concluded that the free radicals produced from the water attack each half at approximately equal rates.
γ-Radiolysis of a mixed disulfide, cysteine-cysteamine disulfide, in unbuffered aqueous solution (0.3 mM) was investigated in the presence and absence of oxygen. The principal products were the thiols (cysteine and cysteamine), the corresponding sulfinic and sulfonic acids, the symmetrical disulfides (cystine and cystamine) and ammonia. Cystine and cystamine were formed in very high yields in deaerated solution; (G(CySSCy) ~ 15) but addition of oxygen reduced the yield sharply and it was inversely proportional to the oxygen concentration except at very low oxygen levels. In aerated solution G(CySSCy) = 0.8. These observations were attributed to a chain reaction which was suppressed by oxygen:[Formula: see text]In the case of proteins, it was concluded that although chain reactions between RS• radicals and protein disulfide bonds were possible, they should be inhibited by oxygen.