The 60Co gamma-radiolysis of aqueous papain solutions: repair and protection by cysteine.

The present work confirms the earlier observations that the cysteine proteinase, papain, exhibits a high radiosensitivity and that a large percentage of the inactivation is repaired by cysteine. Papain's radiosensitivity is demonstrated by dose-inactivation plots and by total inactivation yields (G values) in the range 2-6 for solutions saturated with ${\rm N}_{2}{\rm O},{\rm N}_{2}$ , and air at 0°C. The assay of inactivated papain with and without a postirradiation preassay treatment with $3.6\times 10^{-4}$ M cysteine provides a means of assessing the degree of repairable and nonrepairable inactivation and indicates that 25-70% of the inactivated papain may be repaired depending upon the irradiation conditions chosen. At 30°C, the repair process was essentially complete in approximately 5 minutes. Cysteine present in the papain solution during irradiation eliminated both repairable and nonrepairable inactivation. From a comparison of the yields in N2 O and N2 sa...