Direct Voltammetry and Catalysis with Mycobacterium tuberculosis Catalase−Peroxidase, Peroxidases, and Catalase in Lipid Films

Stable films of dimyristoylphosphatidylcholine and M. tuberculosis catalase−peroxidase (KatG), several peroxidases, myoglobin, and catalase showed reversible Fe^III/Fe^II voltammetry on pyrolytic graphite electrodes and catalytic current for hydrogen peroxide and oxygen. Amperometric responses for these films to H₂O₂ at 0 V are likely to contain significant contributions from catalytic reduction of oxygen produced during the catalytic cycles. Relative apparent turnover rates at pH 6 based on steady-state currents at 0 V versus SCE in the presence of H₂O₂ were in the order horseradish peroxidase > cytochrome c peroxidase (CcP) > soybean peroxidase > myoglobin > KatG > catalase. Lower currents for the very efficient peroxide scavengers KatG and catalase may be related to the instability of their compounds I in the presence of H₂O₂. KatG catalyzed the electrochemical reduction of oxygen more efficiently than catalase and CcP but less efficiently than the other peroxidases. DMPC films incorporating glucose oxidase and peroxidases gave good analytical responses to glucose, demonstrating the feasibility of dual enzyme−lipid films for biosensor fabrication.