Abstract
Activity of papain was inhibited by incubating with CySH, GSH or thiol form of thiamine in the presence of a catalytic amount of aquocobalamin (OH-B_<12>) or cyanocobinamide (Factor B). On the contrary, the inhibition of papain by OH-B_<12> in the presence of the disulfides of these thiols was scarecely observed. The inhibition was completely suppressed by the addition of catalase. The loss of thiol groups in the inhibited papain corresponded to the decrease of the enzyme activity. The inhibited papain was completely reactivated by treatment with CySH. When the papain inhibited by the reaction with OH-B_<12> and thiol-thiamine was treated by Na_2S_2O_3,thiamine was released from the enzyme. From these results it was concluded that OH-B_<12> and Factor B catalyze the formation of mixed disulfides between small molecular thiols and papain.
