Methyl-CoM reductase

In the first step of the reductive branch of this metabolic pathway three out of four methyl groups are transferred from methanol to CoM-SH (13) by methyl transferases, with formation of methyl-S-CoM (21) (Scheme 1) [21]. The transformation of 21 and CoB-SH (15) into methane and CoB-S-S-CoM (22) is catalyzed by the methyl-CoM reductase. Again, reductive cleavage of 22 is mediated by the heterodisulfide reductase [22]. The oxidative part involves oxidation of... 

Methylbenzene halogen complex of, 3 122 iodine monochloridecomplese, 3 109 Methylchlorosilanes hydrolysis, 42 149-150, 157 pyrolysis products of, 7 356-363 Methylcobalamin, 19 151, 152 Methyl-coenzyme M reductase, 32 323-325 EPR spectra, 32 323, 325 F43 and, 32 323-324 function, 32 324-325 Methyl-CoM reductase, 32 329 Methyl cyanide, osmium carbonyl complexes, reaction, 30 198-201 Methylcyclophosphazene salts, 21 70 synthesis, 21 109... 

Nickel is found in at least four enzymes urease, certain hydrogenases, methyl-CoM reductase (in its cofactor F430) of methanogenic bacteria, and carbon monoxide dehydrogenase of acetogenic and methanogenic bacteria 434... 

Albracht et al. (90) have observed an EPR spectrum from whole cells of M. thermoautotrophicum (Fig. 13) which appears to arise from protein-bound F430. The same type of spectrum was also observed in purified methyl-CoM reductase. The paramagnetic species on whole cells was only partially reduced by treatment with hydrogen and was unaffected by carbon monoxide. Gel filtration showed it to be part of a soluble protein. The spectrum was somewhat broadened by substitution... 

Tucci and Holm [163] have demonstrated an alternative reaction scheme, starting from the complex [NIi(bpy)(CH3)2(SR")2], where bpy is 2,2 -bipyridyl and R" is aromatic. In this case, the thiol displaced one methyl group from the nickel as methane, in a reaction reminiscent of methyl-CoM reductase, and coordinated to the nickel. Further addition of CO liberated CH3COSR" in high yield. This reaction demonstrates the feasibility of a reaction in which both the thiol and acetyl groups coordinate the nickel. 

CoA = Coenzyme A CoM = Coenzyme M, 2-thioethane-sulfonate ENDOR = Electron nuclear double resonance EPR = Electron paramagnetic resonance H4MPT = Tetra-hydromethanopterin HS-HTP = N-7-mercaptoheptanoyl-O-phosphothreonine MCR = Methyl-CoM reductase MRF = Methyl-reducing factor XAS = X-ray absorption spectroscopy GSH = Glutathione. 

Methyl-CoM Reductase Methyl-SCoM 4- CoBSH — CH4 4- CoBS-SCoM (5)... 

Methyl-CoM reductase subunit a (M) mcrA X07794, Ml8969 22... 

Methyl-CoM reductase operon protein C (M) mcrC XI5364, X05482 14... 

H2, CO dehydrogenase (CODH) interconverts CO and CO2, acetyl-CoA synthetase (ACS) in concert with CODH converts CO2 and a methyl group to acetyl-CoA and methyl-CoM reductase (MCR) generates methane. 

S. W. Ragsdale, Biochemistry of methyl-CoM reductase and coenzyme F430, in The Porphyrin Handbook, K. M. Kadish, K. M. Smith, R. Guilard, (ed.), Academic Press, Amsterdam, 2003, 11, 205-228. 

Among the reactions in the C cycle mentioned above, those that liberate enough free energy to form ATP are those catalyzed by methyl CoM reductase [reaction (6.2)] and H2 heterodisulfide oxidoreductase [reaction (6.3)] (Heiden et al., 1993). In the cycle, no organophosphate compounds are found, which can be the intermediate for ATP biosynthesis as observed in the fermentation. 

Fig. 6.5. A schematic presentation of the Ci cycle (prepared on the basis of Rouviere and Wolfe, 1988 Thauer and Bonacker, 1994 Vaupel and Thauer, 1998). Circled numbers 1, formylmetha-nofuran dehydrogenase (contains Fe/S, and Mo, or W) 2, formylmethanofuran-tetrahydrometha-nopterin A-formyltransferase 3, methenyltetrahydromethanopterin cyclohydrolase 4, methylenetetrahydromethanopterin dehydrogenase 5, methylenetetrahydromethanopterin reductase 6, tetrahydromethanopterin S-methyltransferase (contains Fe/S and vitamin B12) 7, methyl-CoM reductase (contains F430) 8, H2 heterodisulfide oxidoreductase...

Finally, methane is formed from methyl CoM by the catalysis of methyl CoM reductase (Ferry, 1992). When acetyl group (CH3CO-) is decomposed to methyl group (CH3-) and carbon monoxide on the CODH complex molecule, carbon monoxide reacts with water, and electrons are released. The electrons are used for the... 

Ellermann J, Hedderich R, Bocher R, Thauer RK (1988) The final step in methane formation. Investigations with highly purified methyl-CoM reductase (component C) from Methanobac-terium thermoautotrophicum (strain Marburg). Eur J Biochem 172 669-677 Ellfolk N, Sievers G (1974) Correction of the amino acid sequence of soybean leghemoglobin alpha. Acta Chem Scand B 28 1245-1246... 

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