Dithiolato-Bridged Dinuclear Iron-Nickel Complexes [Fe(CO)_2(CN)_2(mu-SCH_2CH_2CH_2S)Ni(S_2CNR2_)]~- Modeling the Active Site of [NiFe] Hydrogenase

摘要

Hydrogenase is essential to hydrogen metabolism by catalyzing the reversible interconversion of proton and molecular hydrogen.The enzyme has been found in many microorganisms of biotech-nological interest,which can be grouped into two classes based on the type of metal-containing active sites,namely,[Fe]-only and [NiFe] hydrogenases.For the [NiFe] hydrogenase,X-ray structure determination has been carried out for Desulfovibrio (D.) gigas,D.fructosovorans,D.vulgaris (Miyazaki),and Desulfomicro-bium (Dm.) baculatum,Two forms of the active sites are known.One is referred to as the oxidized form,where Fe and Ni are bridged by two cysteine S and one O atoms with relatively long Fe-Ni distances of ca.2.9 A.The other is the reduced form,with short Fe-Ni bonds of 2.5-2.6 A and only two bridging cysteine S atoms or perhaps with an additional H-bridge.An exception may be the oxidized form of D.vulgaris (Miyazaki),in which the triply bridged Fe-Ni distance is as short as 2.6 A.Despite the geometrical diversity,interesting common features can be seen in the structure of [NiFe] hydrogenases;the Fe center carries both CO and CN ligands,and the four cysteine S atoms (or three cysteine S atoms and one selenocysteine Se for Dm.baculatum) are coordinated to Ni in a distorted tetrahedral geometry.