Ni-elimination from the active site of the standard [NiFe]­hydrogenase upon oxidation by O2.

Hydrogenase is a key enzyme for a coming hydrogen energy society, because it has strong catalytic activities on both uptake and production of dihydrogen. We, however, have to overcome the sensitivity against O2 of the enzyme, because hydrogenase is, generally, easily inactivated in the presence of O2. In this study, we have revisited the crystal structures of [NiFe]­hydrogenase from sulfate-reducing bacterium in the several oxidized and reduced conditions. Our results revealed that the Ni-Fe active site of the enzyme exposed into O2 showed two forms, Form-1 and Form-2. The Ni-Fe active site in Form-1 showed the typical Ni-B (inactive ready) structure, whereas those in Form-2 lost Ni with no relation to an exposure time to O2, and two cysteinyl sulfur ligands made a disulfide bond. On the other hand, the formation of sulfenylation of the cysteinyl ligand to Ni, which is often observed in the oxidized form, did not correlate with the Ni-elimination, but with exposure time to O2.