Nickel–Iron Hydrogenases

Ni–Fe hydrogenases catalyze the cleavage or the production of the most simple of chemical compounds, molecular hydrogen. This review provides an overview of the literature on these enzymes that has been published before the year 2000. On the basis of atomic models plausible pathways of substrates and products are described, including a hydrophobic tunnel network for H2 diffusion, a suitable arrangement of three iron–sulfur clusters for electron transfer, a network of buried water molecules, and a magnesium site that could be involved in proton transfer. A combination of protein crystallography, electron paramagnetic resonance, and Fourier transform infrared spectroscopic studies has allowed the elucidation of the unique architecture of the active site. This consists of a thiolate-coordinated Ni–Fe unit involving one carbon monoxide and two cyanide ligands to the iron, leaving two metal coordination sites available for substrate binding. Understanding the catalytic mechanism of these fascinating enzymes might be helpful for the development of cheap catalysts for fuel cells working on H2 or of cheaper production methods for this clean fuel. 3D Structure Keywords: hydrogenases; hydrogen metabolism; hydrogen activation; nickel-containing enzyme; redox proteins; electron and proton transfer