Effects of superoxide dismutase, dithiothreitol and formate ion on the inactivation of papain by hydroxyl and superoxide radicals in aerated solutions.

Losses in enzyme activity and sulphydryl content have been studied in aerated papain solutions containing formate, superoxide dismutase and dithiothreitol. Both formate and dithiothreitol converted .OH to .O2-, whereas superoxide dismutase completely suppressed the inactivation by .O2-. Using results from all three systems, the fraction of .O2- reactions with papain that caused inactivation of the enzyme was 0.33 +/- 0.07. The results also showed that the fraction of .OH reactions, which cause inactivation of papain, is significantly higher in aerated than in oxygen-free solutions.