Fundamentals and electrochemical applications of [Ni-Fe]-uptake hydrogenases

Hydrogenases are found in a wide range of archaea, prokaryotes and eukaryotes as soluble and membrane-bound enzymes and are generally classified by the structure of the catalytic site. From a biotechnological perspective, hydrogenases have been examined for their role in the production of biohydrogen; for co-factor regeneration in coupled enzyme reactions; for environmental applications, and for the electrochemical oxidation of molecular hydrogen. Hydrogenases, with their ability to readily oxidise hydrogen or reduce protons into hydrogen, have huge potential as biocatalysts in many emerging technologies based on the use of hydrogen as a clean energy vector. This review will focus on the hydrogenases associated with the oxidation of molecular hydrogen (so-called uptake hydrogenases (EC 1.12.99.6)), covering their properties, structure, isolation, and remaining barriers for potential industrial applications, including bio-fuel cells, photocatalytic water splitting and hydrogen sensors.