Hydrogenases—Biological

Abstract

Abstract Hydrogenases are enzymes that produce or consume hydrogen gas. Each type of hydrogenase contains, as a minimum, an iron atom, with CO and CN ligands which tune its redox potential and Lewis‐acidity to optimize the binding of dihydrogen. The Fe‐hydrogenase from methanogenic bacteria is the simplest hydrogenase and catalyzes a direct hydride transfer from H 2 to its organic substrate. All other hydrogenases catalyze reduction of electron acceptors, according to the equation H 2 = H + + 2 e − . The hydrogen‐binding sites are of two types: the [NiFe(Se)]‐hydrogenases, which contain a dinuclear center of nickel and iron, and the [FeFe]‐hydrogenases, which contain a dinuclear iron site, the H cluster. In each case, the protein is arranged to leave a vacant position in the active site for binding H 2 , as well as separate channels for transfer of H 2 and H + to the surface. A chain of iron‐sulfur clusters provides a pathway for electrons to a binding site on the surface for electron acceptors and donors. O 2 and CO are inhibitors that bind to the vacant site and block access to H 2 ; O 2 also causes oxidation of the metal centers and sulfur ligands. Some hydrogenases from aerobic bacteria, which are resistant to this inhibition, are of interest for applications in biofuel cells.

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Identifiers

DOI

10.1002/0471227617.eoc112

Journal

Encyclopedia of Catalysis

Year

2010