Nickel NiFe -Hydrogenases

The [NiFe] hydrogenase from D. gigas has been used as a prototype of the [NiFe] hydrogenases. The enzyme is a heterodimer (62 and 26 kDa subunits) and contains four redox active centers one nickel site, one [3Fe-4S], and two [4Fe-4S] clusters, as proven by electron paramagnetic resonance (EPR) and Mosshauer spectroscopic studies (174). The enzyme has been isolated with different isotopic enrichments [6 Ni (I = I), = Ni (I = 0), Fe (I = 0), and Fe (I = )] and studied after reaction with H and D. Isotopic substitutions are valuable tools for spectroscopic assignments and catalytic studies (165, 166, 175). 

Most of the as-isolated [NiFe] hydrogenases are inactive, and the nickel center exhibits an intense rhombic EPR signal termed Ni-A (g = 2.31, 2.26, and 2.02) with variable amounts of a second nickel species, named Ni-B (g = 2.33, 2.16, and 2.02), with slightly different... 

Wang C-P, R Franco, JJG Moura, 1 Moura, EP Day (1992) The nickel site in active Desulfovibrio baculatus [NiFeS] hydrogenase is diamagnetic. Multifield saturation magnetization measurement of the spin state of Ni(II). 7 Sio/ Chem 267 7378-7380. 

Nickel is found in thiolate/sulflde environment in the [NiFe]-hydrogenases and in CODH/ACS.33 In addition, either a mononuclear Ni-thiolate site or a dinuclear cysteine-S bridged structure are assumed plausible for the new class of Ni-containing superoxide dismutases, NiSOD (A).34 [NiFe]-hydrogenase catalyzes the two-electron redox chemistry of dihydrogen. Several crystal structures of [NiFe]-hydrogenases have demonstrated that the active site of the enzyme consists of a heterodinuclear Ni—Fe unit bound to thiolate sulfurs of cysteine residues with a Ni—Fe distance below 3 A (4) 35-39 This heterodinuclear active site has been the target of extensive model studies, which are summarized in Section 6.3.4.12.5. 

Bradyrhizobium japonicum [NiFe] hydrogenase Membrane-bound cytochrome b reducing Energy conservation H2 recyling during N2 fixation H2,Q2, nickel, carbon and energy source limitation 3... 

All these experimental results point unambiguously to a heterobimetallic catalytic centre in [NiFe] hydrogenases, which thus deserve their previously assigned name (Moura et al. 1988). Anomalous diffraction has been successfully used also to identify the selenium atom of the selenocysteine binding to the nickel atom in Dm. baculatum (Garcin et al. 1999). 

Although hitherto no structural analogue of the complete heterodimetallic nickel-iron centre of [NiFe] hydrogenase has been reported, some compounds with similarities to the biological centre were recently synthesized using specially designed... 

Davies, S. C., Evans, D. J., Hughes, D. L., Longhurst, S. and Sanders, J. R. (1999) Synthesis and structure of a thiolate-bridged nickel-iron complex Towards a mimic of the active site of NiFe-hydrogenase. Chem. Commun., 1999, 1935-6. 

Kruger, H.-J., Peng, G. and Holm, R. H. (1991) Low-potential nickel(III,II) complexes - new systems based on tetradentate amidate thiolate ligands and the influence of ligand structure on potentials in relation to the nickel site in [NiFe]-hydrogenases. Inorg. Chem., 30, 734-42. 

Maier, T. and Bock, A. (1996) Generation of active [NiFe] hydrogenase in vitro from a nickel-free precursor form. Biochemistry, 35, 10089-93. 

Menon, A. L. and Robson, R. L. (1994a) In vivo and in vitro nickel-dependent processing of the [NiFe] hydrogenase in Azotohacter vinelandii. ]. Bacterial., 176, 291-5. 

Sellmann, D., Geipel, F. and Moll, M. (2000) [Ni(NHPnPr3)(S3)], the first nickel thiolate complex modeling the nickel cysteinate site and reactivity of [NiFe] hydrogenase. Angew. Chem. Int. Ed. Engl., 39, 561-3. 

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