Hydrogenases, Structure and Function

Hydrogenase catalyzes the reversible oxidation of dihydrogen. They can be divided into three phylogenetically distinct classes, that is, [NiFe], [FeFe], and [Fe] hydrogenases, according to the type of catalytically active metal center. Whereas most [NiFe] hydrogenases are of the hydrogen uptake type, [FeFe] hydrogenases mainly produce molecular hydrogen and [Fe] hydrogenases catalyze a specific reaction utilizing H 2 . Crystallographic structures of hydrogenases from all three classes have been determined at atomic resolution and have given insight into the possible pathways for the transfer of electrons, protons, and gaseous molecules such as dihydrogen. In [NiFe] and [FeFe] hydrogenases, the electrons are transferred via chains of iron–sulfur centers, whereas the [Fe] hydrogenases have no iron–sulfur centers. All three classes of hydrogenases contain at least one iron atom in the active site, which carries unusual nonprotein diatomic ligands, such as carbon monoxide and cyanide. A common mechanism of all three types of hydrogenases for the heterolytic splitting of dihydrogen has been proposed that takes place at a dinuclear X-Fe center. The only variable is the first cation X which can be a nickel, an iron, or a carbon in the three classes of hydrogenases.