The Structure of the D. gigas [NiFe] Hydrogenase and the Nature of the Hydrogenase Nickel Complex

Several surprises came to light in the recent single‐crystal X‐ray structural determination of a [NiFe] hydrogenase by Volbeda et al. For example, the Ni fraction of the enzyme clearly forms part of an unprecedented cysteine‐bridged heterometallic binuclear system. In retrospect, the feasibility of such a structural motif is evident from the known coordination chemistry of nickel thiolate complexes. But the mechanism of H2 oxidation by this NiFe(?) complex remains tantalizingly opaque and continues to challenge bioinorganic chemists.