Activation of oxidized cysteine proteinases by thioredoxin-mediated reduction in vitro.

Activity of the cysteine adducts of the cysteine proteinases papain and thaumatopain can be recovered by treatment with thioredoxin, thioredoxin reductase and NADPH. Recovery of proteinase activity did not occur if any of the components of the thioredoxin system were omitted, or if thioredoxin or thioredoxin reductase were heat-inactivated. Such an enzyme-mediated process may be of significance in the recovery of cysteine proteinases inactivated by oxidative attack.