Hydrogenase and

Oxidoreduciases. Enzymes catalysing redox reactions. The substrate which is oxidized is regarded as the hydrogen donor. This group includes the trivially named enzymes, dehydrogenases, oxidases, reductases, peroxidases, hydrogenases and hydroxylases. 

Hydrogenase and its application for photoinduced hydrogen evolution. I. Okura, Coord. Chem. Rev., 1985,68,53 (141). 

NICKEL-IRON-SULFUR ACTIVE SITES HYDROGENASE AND CO DEHYDROGENASE... 

The biologically uncommon Ni center associated with FeS clusters is a powerful and unique catalytic unity. In this chapter we have reviewed the structural and mechanistic aspects of three NiFeS centers the active site of hydrogenase and Clusters A and C of CODH/ACS. In the former, the association of a Ni center with the most unusual FeCOCN2 unit is a fascinating one. Model chemists, spectroscopists, and crystallographers have joined efforts to try and elucidate the reaction mechanism. Although a consensus is being slowly reached, the exact roles of the different active site components have not yet been fully established. Ni appears to be the catalytic center proper, whereas the unusual Fe center may be specially suited to bind a by-... 

In addition, the [NiFe] hydrogenase from D. fructosovorans is very similar to D. gigas hydrogenase, and its structure has been solved 185). In order to understand the role of the [3Fe-4S] cluster, a Pro-432Cys mutant was produced. In this mutant the conversion of a [3Fe-4S] into a [4Fe-4S] center was proven by EPR and X-ray crystallography. 

Fe Q-band ENDOR study of the isotopically enriched Ni-C state of D. gigas and D. desulfuricans hydrogenases and Ni-B state of D. desulfuricans revealed a weak coupling between the Fe and the nickel atoms when the enzyme was in the Ni-A forms while no coupling was observed for the Ni-B form (186). A careful analysis of linewidth of Ni-A and Ni-B EPR signals detected in Fe enriched and nonenriched hydrogenase samples indicated that hyperfine interactions are lost in the spectral linewidth and, hence, nonde-tectable. 

We will use here the main results obtained for two complex and distinct situations the structural and spectroscopic information gathered for D. gigas [NiFe] hydrogenase and AOR, in order to discuss relevant aspects related to magnetic interaction between the redox centers, intramolecular electron transfer, and, finally, interaction with other redox partners in direct relation with intermolecular electron transfer and processing of substrates to products. 

Laska S, F Lottspeicht, A Kletzin (2003) Membrane-bound hydrogenase and sulfur reductase of the hyper-thermophilic and acidophilic archaeon AcidiawMi ambivalens. Microbiology (UK) 149 2357-2371. 

Leger C, Jones AK, Albracht SPJ, Armstrong FAA. 2002. Effect of a dispersion of interfacial electron transfer rates on steady state catalytic electron transport in [NiFe]-hydrogenase and other enzymes. J Phys Chem B 106 13058-13063. 

FeFe]-hydrogenase and models HRed. Clostridium pasteurianum 4.2 0.08 0.87 [310]... 

NiFe]-hydrogenase and models State D, Chromatium vinosum 4.2 0.05-0.15 [314]... 

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. 

The interest in low-valent Ni complexes in S-rich environments has been stimulated by the presence of Ni in [Ni,Fe] hydrogenase and CODH. While thiolate ligation usually favors higher oxidation states, thioethers stabilize Ni1 and Ni°. In most cases, however, Ni1 ions of an NiS4 chromophore are unstable with respect to disproportionation. The cyclic voltam-mogram of square planar (983) with homoleptic thioether coordination exhibits a quasi-reversible wave at —0.42V (vs. NHE), which on the basis of the rhombic EPR spectrum (gi 2.27, g2 2.11, and g3 2.03) of the chemically reduced species (Na/Hg) is assigned to metal-centered reduction. 8... 

Hydrogenase and other components of the N2 fixing apparatus of bacteria have been shown to be non-heme iron proteins (66). 

Hydrogenase and CO Dehydrogenase Juan C. Fontecilla-Camps and Stephen W. Ragsdale... 

Raising the incubation temperature from 45 to 57°C did not bring about a pronounced increase of the hydrogen-driven pMMO activity. This preliminary observation indicated in vivo heat stability of the hydrogenase and pMMO activities. The temperature dependent difference in the solubility of hydrogen may also explain the small activity difference, particularly as similar results were obtained for the hydrogen-driven sMMO activity. 

Y. P. Chen, D. C. Yoch (1987) Regulation of two nickel-requiring (inducible and constitutive) hydrogenases and their coupling to nitrogenase in Methylosinus trichosporium OB3b. J. Bacteriol., 169 4778-4783... 

The design of complex NiFe compounds which mimic active site of hydrogenase and have the catalytic activity comparable with pure enzyme. 

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