On the Mechanism of Peroxidase-Catalyzed Oxygen Production

A mechanism for oxygen production involving the reaction of cation radicals with H2O2 was investigated. The rate of oxygen production by peroxidases was greatly enhanced by the addition of ABTS [2,2′-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid)] or chlorpromazine, both of which are oxidized to cation radicals by peroxidases. We propose that enhanced oxygen evolution is due to the reaction of the cation radicals of these compounds with H2O2 to produce O⨪2 which then dismutates to produce oxygen. Oxygen evolution was quantitated in reaction mixtures containing electrochemically generated ABTS cation radicals and H2O2. The reaction was found to be first order with respect to the concentrations of the ABTS cation radical and H2O2 and the rate constants indicated that O⨪2 was an intermediate. Ferric EBTA enhanced oxygen production in both reaction systems (i.e., using ABTS+·that was generated electrochemically or with a peroxidase). These results suggest that O⨪2 production catalyzed by peroxidases is dependent upon a compound which is oxidized by the peroxidase to a cation radical. Superoxide is subsequently produced from the one-electron oxidation of H2O2 by the cation radical.