An alternative mechanism for catalase activity

The ferric heme active sites of enzymes such as catalases and peroxidases react with hydrogen peroxide to generate a "high-valent" ( formally, Fe( V)) species, known as Compound I. In peroxidases, Compound I generally decays back to the ferric state by abstracting electrons from various organic substrates or redox proteins. In catalases, the electrons required for Compound I reduction are supplied by a second H2O2 molecule. It has long been implied that the reaction between Compound I and H2O2 in catalase implies either outer-sphere electron transfer and/or hydrogen/proton abstraction mechanisms. Recent DFT calculations have confirmed that such mechanisms may be viable. However, a recent experimental investigation by Obinger and co-workers now prompts us to investigate an alternative mechanism, whereby the oxygen atom in Compound I is substituted by a second peroxide molecule, generating a formally Fe(V)-peroxo adduct which by electromerism would convert to Fe(III) and liberate the final product, O-2. Reported here are DFT calculations illustrating the theoretical viability of this newly proposed catalase mechanism.