Sulfur-nickel-iron proteins

CODH/ACS is an extremely oxygen-sensitive protein that has been found in anaerobic microbes. It also is one of the three known nickel iron-sulfur proteins. Some authors would consider that there are only two, since the CODH and ACS activities are tightly linked in many organisms. However, there is strong evidence that the ACS and CODH activities are associated with different protein subunits and the reactions that the two enzymes catalyze are quite different. CODH catalyzes a redox reaction and ACS catalyzes the nonredox condensation of a methyl group, a carbonyl group, and an organic thiol (coenzyme A). 

This enzyme [EC 1.18.99.1], also known as hydrogenly-ase, catalyzes the reaction of H2 with two oxidized ferre-doxin to produce two H+ and two reduced ferredoxin. This enzyme is an iron-sulfur protein and requires nickel ions. It can use molecular hydrogen to reduce a variety of substances. See also Hydrogen Dehydrogenase Cytochrome C3 Hydrogenase... 

It is not known at present if the nickel is coordinated directly to the protein, as in copper and iron-sulfur proteins, or to an organic cofactor, as in the molybdenum hydroxylases and hemoproteins. 

Kumar, M., Lu, W.-P., and Ragsdale, S. W., 1994, Binding of carbon disufide to the site of acetyl-CoA synthesis by the nickel-iron-sulfur protein, CO dehydrogenase, from Clostridium thermoaceticum, Biochem. 33 976999777. 

Ragsdale, S. W., Clark, J. E., Ljungdahl, L. G., Lundie, L. L., and Drake, H. L., 1983, Properties of purified carbon monoxide dehydrogenase from Clostridium thermoaceticum a nickel, iron-sulfur protein, J. Biol. Chem. 258 2364n2369. 

Cobalt B12 Enzymes Coenzymes Iron Sulfur Proteins Metallocenter Biosynthesis Assembly Nickel Models of Protein Active Sites. 

Active Sites, Copper Proteins Oxidases, Copper Proteins with Type 1 Sites, Copper Proteins with Type 2 Sites, Copper Enzymes in Denitrification, Iron-Sulfur Models of Protein Active Sites, Iron-Sulfur Proteins Nickel Enzymes Cofactors and Nickel Models of Protein Active Sites). However, since many metalloenzymes have been found or postulated to incorporate metal-sulfur bonding, it is appropriate that a very short sununary be included here. 

The acidification of H2 may also be involved in hydrogenase action, where H2 is beheved to bind to an Fe(II) center. Isotope exchange between H2 and D2O is catalyzed by the enzyme see Nickel Enzymes Cofactors Nickel Models of Protein Active Sites Iron-Sulfur Proteins). Similar isotope exchange can also occur in H2 complexes. Oxidative addition to give a classical dihydride is also a common reaction. [W(H2)(CO)3(PCy3)2] is in equilibrium with about 20% of the dihydride in solution. This can lead to subsequent hydrogenolysis of M-C bonds as in the case of a cyclometallated phenylpyridine complex of Ir(III). ... 

The final step in methanogenesis is the reductive demethylation of CH3-S-CoM to CH4. This reduction involves two reactions CH3-S-C0M is reduced with jV-7-mercaptoheptanoylthreonine phosphate (H-S-HTP) (Fig. 2B) as electron donor to yield CH4 and a heterodisulfide of H-S-CoM and H-S-HTP (CoM-S-S-HTP) (Reaction 7, Table 2). This reaction is catalyzed by CH3-S-C0M reductase [70-72] which contains a nickel porphinoid, factorF430, as prosthetic group (Fig. 2C) (for a recent review see Friedmann et al. [73]). The subsequent reduction of the heterodisulfide with H2 to yield H-S-HTP and H-S—CoM (Reaction 8, Table 2) is catalyzed by CoM-S-S-HTP-dependent heterodisulfide reductase. The enzyme is an iron-sulfur protein containing FAD as prosthetic group [74]. The physiological electron donor for the heterodisulfide reductase is not known. 

Calcium-binding Proteins Copper Enzymes in Denitrification Copper Proteins with Type 1 Sites Copper Proteins with Type 2 Sites Iron Heme Proteins Electron Transport Iron-Sulfur Proteins Metal-mediated Protein Modification Metallochaperones Metal Ion Homeostasis Molybdenum MPT-containing Enzymes Nickel Enzymes Cofactors, Nitrogenase Catalysis Assembly Zinc Enzymes. 

In dealing with such a vast domain some decisions concerning the subjects addressed in this short chapter had to be made. Consequently, only selected enzymes containing the transition metals copper, iron, manganese, molybdenum/ tungsten, nickel and the related zinc, will be discussed also, we will consider only X-ray structures of active sites published relatively recently and for which some discussion on the catalytic mechanism is included. Some reference is also made to Co in the context of the correnoid iron sulfur protein that interacts with acetyl Coenzyme A synthase in the synthesis or cleavage of acetyl CoA. With a few exceptions, the protein structure beyond the metal coordination sphere will not be described unless it impinges in the catalytic mechanism. 

This review concerns proteins that contain both nickel and iron. Below are listed the three known proteins of this class and the reactions that they catalyze. The active sites of all of these consist of het-erometallic nickel-iron-sulfur (NiFeS) clusters. The terms used will he explained later in the text. 

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