Enhanced Oxygen-Tolerance of the Full Heterotrimeric Membrane-Bound [NiFe]-Hydrogenase of Ralstonia eutropha

Abstract

Hydrogenases are oxygen-sensitive enzymes that catalyze the conversion between protons and hydrogen. Water-soluble subcomplexes of membrane-bound [NiFe]-hydrogenases (MBH) have been extensively studied for applications in hydrogen–oxygen fuel cells as they are relatively tolerant to oxygen, although even these catalysts are still inactivated in oxidative conditions. Here, the full heterotrimeric MBH of Ralstonia eutropha, including the membrane-integral cytochrome b subunit, was investigated electrochemically using electrodes modified with planar tethered bilayer lipid membranes (tBLM). Cyclic voltammetry and chronoamperometry experiments show that MBH, in equilibrium with the quinone pool in the tBLM, does not anaerobically inactivate under oxidative redox conditions. In aerobic environments, the MBH is reversibly inactivated by O2, but reactivation was found to be fast even under oxidative redox conditions. This enhanced resistance to inactivation is ascribed to the oligomeric state of MBH in the lipid membrane.

Mechanism of Protection of Catalysts Supported in Redox Hydrogel Films

“…3,15 In these cases the protection mechanism seems to result from reductive reactivation by the mediators or adjacent hydrogenase molecules. In the case that we considered, the film can protect the enzyme even if the inactivation is irreversible (k r can be zero), and the value of the rate constant for the inhibition reaction k i does not determine the resistance to O 2 either.…”

“…3 However, a crucial and unique feature of the system we investigate, which has no correspondence in vivo, is the spatial separation, within the depth of the film, between the enzyme that gives electrons to the electrode and the enzyme that produces the electrons that quench dioxygen.…”

Biohydrogen for a New Generation of H2/O2 Biofuel Cells: A Sustainable Energy Perspective

“…Finally, elegant work from Jeuken et al recently demonstrated the immobilization of the same trimeric complex at gold electrodes modified with tethered bilayer lipid membrane. [145] Not only was a fast reactivation of the enzyme at high potentials after aerobic stress obtained, but also no anaerobic inactivation at high redox potential occurred. These properties may be linked to the oligomeric state of MbH in the lipid membrane.…”

Pushing the limits for enzyme-based membrane-less hydrogen fuel cells – achieving useful power and stability

“…[1][2][3][4][5][6][7] Not only do enzymes prove the feasibility of replacing platinum metal catalysts with ones derived from abundant elements (indeed the active sites of enzymes are more active than Pt [8][9][10][11] ) but their high selectivity lends itself to simple, membrane-less fuel cells that could be miniaturized, thus compensating for the large footprint of the catalyst. [1][2][3][4][5][6][7] Not only do enzymes prove the feasibility of replacing platinum metal catalysts with ones derived from abundant elements (indeed the active sites of enzymes are more active than Pt [8][9][10][11] ) but their high selectivity lends itself to simple, membrane-less fuel cells that could be miniaturized, thus compensating for the large footprint of the catalyst.…”