Kinetic Analysis of Inactivation and Enzyme Reaction of Oxygen-Tolerant [NiFe]-Hydrogenase at Direct Electron-Transfer Bioanode

Abstract

Abstract Membrane-bound [NiFe]-hydrogenase (MBH) from Hydrogenovibrio marinus is an O2-tolerant enzyme and allows direct-electron-transfer (DET) bioelectrocatalysis for H2-oxidation. MBH is a promising bioelectrocatalyst for bioanode of enzymatic H2–O2 biofuel cells. From the practical viewpoint of electricity production, the H2-depletion near the electrode surface and the oxidative and reversible inactivation called “anaerobic inactivation” of [NiFe]-hydrogenases limit the H2-oxidation at high potentials. We have already proposed a gas-diffusion system to avoid inactivation in our previous study. In this research, we have analyzed the kinetics of the electrochemically induced anaerobic inactivation and the DET bioelectrocatalytic reaction of MBH on electrodes. When the inactivation is considered as a competitive inhibition-like reaction, the maximum value of the apparent Michaelis constant reaches 6.5 mM (at Ketjen Black-modified electrode) as analyzed in our kinetic model. Since the value is larger than the saturated H2-concentration in solution (0.74 mM), we conclude that high-speed H2-supply realized by a gas-diffusion electrode is essential to compete with the inactivation. Furthermore, a gas-diffusion bioanode with MBH can eliminate the H2-depletion near the electrode surface and has reached about 10 mA cm−2 at 0 V (vs. Ag|AgCl|sat. KCl electrode) under quiescent (passive) and H2-atmospheric conditions.