Nickel-containing enzymes hydrogenase

In contrast to the abundance of Fe-proteins, there are only six known nickel-containing enzymes hydrogenase, CO dehydrogenase (CODA), acetyl-CoA synthase (ACS), superoxide dismutase, urease, and S-methyl-CoM methylreductase. Among these enzymes, it exists in very diverse environments, including a dinickel site (urease), a Ni-Fe heterobinuclear site (hydrogenase), a Ni-Fe4S4 heterometallic... 

Graf, E.-G. and Thauer, R. K. (1981) Hydrogenase from Methanobacterium thermoau-totrophicum, a nickel-containing enzyme. FEBS Lett., 36, 165-9. 

Hydrogenases are not the only nickel-containing enzyme, and researchers must therefore compare the maturation of different nickel proteins to obtain an integrated picture of nickel metabolism. Indeed, similarities between some of the hydrogenase-related nickel-processing proteins with urease and carbon monoxide dehydrogenase maturation factors have been noted, and this has facilitated interpretations of the results for... 

Nickel(l) complexes are rather rare, but this oxidatirm state is thought to be involved in the catalytic function of nickel-containing enzymes such as pS[iFe]-hydrogenase (see Fig. 29.19). Dark red K4[Ni2(CN)g] can be prepared by Na amalgam reduction of K2 [Ni(CN)4]. It is diamagnetic and the anion has structure 21.54 in which the Ni(CN)3 units are mutually perpendicular. The reaction of... 

The three-pulse electron spin-echo envelope modulation (ESEEM) technique is particularly sensitive for detecting hyperfine couplings to nuclei with a weak nuclear moment, such as 14N. It has been used to probe the coordination state of nickel in two hydrogenases from M. tkermoautotrophicum, strain AH (56). One of these enzymes contains FAD and catalyzes the reduction of F420 (7,8-dimethyl-8-hydroxy-5-deazaflavin), while the other contains no FAD and has so far only been shown to reduce artificial redox agents such as methyl viologen. 

The soluble hydrogenase from the hydrogen-oxidizing bacterium N. opaca is one of a class of hydrogenases that contain flavin and use nicotinamide adenine dinucleotide (NAD) as electron acceptor. The protein consists of four dissimilar subunits and contains approximately four atoms of nickel, one FMN, three [Fe-4S] clusters, one [2Fe-2S] cluster, and up to one [3Fe-xS] cluster (82). Two of the nickel atoms were readily removed by dialysis, in contrast to the nickel in most hydrogenases. The enzyme would only catalyze electron transfer from hydrogen to NAD if cations, of which Ni2+ is the most effective, were added. In the absence of the cations, the enzyme could be separated as... 

EPR spectra of CO oxidoreductase under non reducing conditions showed a spectrum at g = 2.21, 2.11, and 2.02, which, by analogy with spectra observed in nickel-containing hydrogenases, was attributed to Ni(III) (96). The spectrum was of low intensity and it was not established whether it represents an active state of the enzyme. 

Many microbes contain a hydrogenase that lacks nickel. The best studied of these proteins is the hydrogenase from C. pasteurianum (Adams, 1990). The active site of this protein has been called the H cluster. Two structures of this protein recently appeared, a 1.6 structure of the het-erodimeric Desulfovibrio desuljuricans enzyme (Nicolet et al., 1999) and the 1.8 structure of the Cpl enzyme from Clostridium pasteurianum (Peters et al., 1998). The H cluster at the active site contains 6Fe as proposed earlier (Adams et al., 1989). There are two subcomponents a typical [4Fe64S] cubane bridged by a cysteine residue to an active site binuclear Fe center (Figure 4b). The unusual nature of the iron site in the NiFe hydrogenase is... 

S. W. Ragsdale, Nickel Containing CO Dehydrogenases and Hydrogenases, in Enzyme-Catalyzed Electron and Radical Transfer , eds. A. Holzenburg andN. Scrutton, Plenum Press, New York, 2000, Vol. 35, p. 487. 

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). 

---