OXIDATIVE DAMAGE TO PROTEOLYTIC-ENZYMES - INACTIVATION OF PAPAIN AND FICIN BY FERRYLMYOGLOBIN

Ferrylmyoglobin [MbFe(IV)=O], formed by activation of metmyoglobin by hydrogen peroxide, inactivates the cysteine proteinases papain (EC 3.4 .22.2) and ficin (EC 3.4.22.3) more efficiently than hydrogen peroxide , but less efficiently than hydroxyl radicals as generated by peroxyni trite nitrite or the Fenton reaction. Metmyoglobin and oxymyoglobin co uld not inactivate papain and ficin. Oxidation of papain and ficin by ferrylmyoglobin occurs in enzyme/ haem-protein complexes with binding constants of approximately 10(5) 1 mol(-1); inactivation of proteolysi s by papain plateaus at neutral pH to about 1/3 whereas the inactivati on under acidic conditions was larger.