ELECTROCHEMICAL GENERATION AND REACTIONS OF FERRYLMYOGLOBINS IN WATERAND MICROEMULSIONS

Ferrylmyoglobin species, which are active oxidant forms of the protein myoglobin, were obtained by electrochemical reduction of metmyoglobin [MbFe(III)] in the presence of oxygen in aqueous neutral buffer and i n microemulsions of oil, water, and cationic surfactant. Reduction of myoglobin at -0.4 V vs SCE catalyzed the reduction of oxygen to hydrog en peroxide at the electrode. Hydrogen peroxide oxidizes metmyoglobin in solution to give the radical ferrylmyoglobin . X-MbFe(IV)=O, which is known to decay rapidly to the non-radical MbFe(IV)=O. This complex reduction-oxidation process converted nearly all of the 30 mu M myoglo bin in a spectroelectrochemical cell to ferrylmyoglobins in 15 min in pH 7.3 buffer and in 18 min in microemulsions. Characteristic ferryl h eme absorbance bands near 421, 548, and 584 nm were used to identify p roducts. Confirmation of ferrylmyoglobins was provided by reductions t o metmyoglobin with ascorbate and by myoglobin-mediated electrochemica l epoxidation of styrene. Fiftyfold higher yields of styrene oxide and benzaldehyde were achieved in a microemulsion compared to electrochem ical or chemical methods in pH 7.4 buffer. The electrochemical approac h described may also prove useful for investigating active catalytic s pecies of heme enzymes such as cytochrome P450.