Analysis of the peroxidatic mode of action of catalase

Catalase is an enzyme which can function either in the catabolism of hydrogen peroxide or in the peroxidatic oxidation of small substrates such as ethanol, methanol, or elemental mercury (Hg0). It has been reported that native catalase can peroxidatically oxidize larger organic molecules (e.g. L-dopa) and that catalase maintained at alkaline pH for various lengths of time demonstrates an increase in peroxidase activity using guaiacol as substrate. We have shown, by using two distinct methods of H2O2 introduction for measuring peroxidase activity, that native catalase shows no peroxidatic activity toward these larger organic molecules. We have also shown, through the use of these peroxidase assays and by enzyme absorption spectra, that the peroxidase activity attributed to catalase maintained at alkaline pH is a catalytic but not enzymatic activity associated with a hematin group attached to a denatured catalase monomer. Possible mechanisms for the catalytic and peroxidatic modes of action of catalase involving hydride-ion transfer are discussed.