The active site and catalytic mechanism of NiFe hydrogenases

This Perspective describes, from our own personal experiences, how the architecture of the NiFe hydrogenase active site has been elucidated by a combination of protein crystallography, Electron paramagnetic resonance and Fourier transform infrared spectroscopic studies. Thus within a period of eight years our perception of the active center has changed from a mononuclear Ni center with S and N/O coordination to a binuclear NiFe unit with thiolate (to Ni and Fe) and CO and CN-(to Fe) ligands. This biologically unusual organometallic cluster poses a real challenge in terms of understanding the role of its different components. Current ideas concerning the NiFe hydrogenase catalytic mechanism are discussed in this context.