Effects of Superoxide Dismutase, Dithiothreitol and Formate Ion on the Inactivation of Papain by Hydroxyl and Superoxide Radicals in Aerated Solutions

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Abstract
Losses in enzyme activity and sulphydryl content were studied in aerated papain solutions containing formate, superoxide dismutase and dithiothreitol irradiated with 60Co. Both formate and dithiothreitol converted .**GRAPHIC**. to .**GRAPHIC**. whereas superoxide dismutase completely suppressed the inactivation by .**GRAPHIC**. Using results from all 3 systems, the fraction of .**GRAPHIC**. reactions with papain that caused inactivation of the enzyme was 0.33 .+-. 0.07. The fraction of .**GRAPHIC**. reactions, which cause inactivation of papain, is significantly higher in aerated than in O2-free solutions.