Methanogene enzyme

In 1984, the first methanogenic CODH was isolated from Methano-sarcina barkeri (138) and was shown to consist of a complex of the a and e subunits, with an apparent molecular mass of 232 kDa. Similar results have been found for other methanogenic CODH preparations (139-143). CODH activity must reside in the a subunit of the methanogenic enzyme, since the e subunit lacks cysteine residues and could... 

In acetate-catabohzing methanogens, enzyme-bound methylcorrinoids are also indicated to serve as intermediates in methyl-group transport. There, methane and carbon dioxide are formed from acetic acid (via acetyl coenzyme A, whose acetyl group is spht into carbon monoxide and a corrin-bound methyl group). Accordingly, the methyl-group... 

For example, incorporation of nickel into carbon monoxide dehydrogenase of Rhodospirillum rubrum requires the prior reduction of an Fe-S cluster. Structural studies of this protein reveal that the added Ni completes a unique [lNi-4Fe-4S] center that is required for activity.Another example of a reductive activation step occurs during NiFe-hydrogenase biosynthesis, perhaps involving participation of the Fe-S cluster in HypD. Yet a third example from the Ni-enzyme literature involves the synthesis of methyl-X-coenzyme M reductase, a methanogen enzyme that contains the Ni-tetrapyrrole cofactor F43q. Formation of active enzyme requires both the reduction of Ni + to NF+ and reduction of a C=N bond in the organic macrocycle. 

Methanogene enzymes reduce CO2 to CH4 and recover the resulting energy. In the last step, methyl-coenzyme M is hydrogenated to methane by a thiol cofactor HS-HTP, the reaction being catalyzed by the nickel enzyme. 

Chistoserdova L, JA Vorholt, RK Thauer, ME Lidstrom (1998) Cl transfer enzymes and coenzymes linking methylotrophic bacteria and methanogenic archaea. Science 281 99-102. 

In Hg-resistant bacteria that are resistant to organic forms of Hg such as phenylmercuric acetate and methylmercury chloride, lyases are involved in the fission of the C-Hg to form Hg + and benzene or methane, and the enzyme has been partly purified (Schottel 1978). The Hg + may then be reduced to nontoxic Hg°. The situation under anaerobic conditions for sulfate-reducing bacteria is complicated by the possibility of both methylation and demethylation in the same strain (Pak and Bartha 1998), plausibly by operation of the acetyl-CoA pathway (Choi et al. 1994 Ekstrom et al. 2003). Under anaerobic conditions, demethylation, though not methylation, has been reported for a methanogen (Pak and Bartha 1998). 

Shima, S., Warkentin, E., Thauer, R.K. and Ermler, U. (2002) Structure and function of enzymes involved in the methanogenic pathway utilising carbon dioxide and molecular hydrogen, J. Biosci. Bioeng., 93, 519-530. 

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