Reactions of H-2 with the nickel site(s) of the [FeNi] and [FeNiSe] hydrogenases: What do the model complexes suggest?

In recent years, the structure(s) of the active site(s) of the nickel-containing hydrogenases (H(2)ases) and the mode of H-2 activation at the nickel site(s) of these enzymes have been explored in detail, In such pursuit, spectroscopic and kinetic measurements have been performed on several H(2)ases. Despite all these data, the mechanism(s) of H-2 assimilation and H-2 evolution by the microorganisms remain rather elusive at the present time. Several groups, including ours, have therefore adopted the modeling approach to elucidate the structure and function of the biological nickel site. This review contains a concise account of the spectroscopic experiments on the enzymes as a background for the subsequent modeling studies, It also provides a comprehensive summary of the modeling work by our group and others. Specific attempts have been made to correlate the spectral and reactivity parameters of good model complexes with those of the H(2)ases and derive conclusions regarding structural and functional characteristics of the biological nickel site.