The active site of the [NiFe] hydrogenase from Desulfovibrio vulgaris Miyazaki F in the oxidized form has been reported as a hetero binuclear Ni-Fe complex with four non-protein ligands (SO, CO, CN, S). In contrast, the non-protein ligands in the hydrogenase from Desulfovibrio gigas were reported as CO, CN, CN and O. The S bridging ligand atom was confirmed by two experiments that the hydrogenase liberates H
2S upon reduction with H
2 and that the crystal structure of the H
2-reduced form lost the bridging ligand between the Ni and Fe atoms. The possible mechanism of the hydrogen activation is discussed.
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