Methane synthetase

MethylmalonylCoA mutase Glutamate mutase a-Methylene-glutarate mutase Dioldehydrase Glyceroldehydrase Ethanoldeaminase L-/3-lysine mutase D-a-lysine mutase Ribonucleotide reductase Methionine synthetase Methane synthetase Methyl transferase Acetate synthetase... 

Among the enzymes implicated in mercury methylation are methionine synthetase, acetate synthetase, and methane synthetase. The last one is a very common enzyme in anaerobic ecosystems, such as lake and river sediments. These enzymatic processes can generate and CHa species where... 

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. 

Selenomethionine metabolism to selenide and the incorporation into selenium-specific proteins may occur by two pathways metabolism to methane selenol and selenide or via selenocysteine. Evidence that the incorporation of selenium from selenomethionine into protein is by the transsulfuration pathway (methionine to cysteine) comes from studies of selenomethionine metabolism in lymphoblast cell lines deficient in cystathionine lyase and cystathionine synthetase, enzymes of the transsulfuration pathway (Beilstein and Whanger 1992). Deficiency in these enzymes greatly reduces the incorporation of selenomethionine into glutathione peroxidase. 

Methylcobalamin also participates as a substrate for an enzymatic reaction in the formation of methane in certain methanogenic bacteria. In this reaction, which can be considered as a model for the second half-reaction of methionine synthetase, the cobalt-bound methyl group is transferred to 2-mercaptoethanesulfonic acid (coenzyme M) [39], the 5-methyl sulfide of which is subsequently reduced to yield methane. Additionally, methylcobalamin participates in the rather obscure process of acetate synthesis in certain bacteria in which it can be shown that the cobalt-bound methyl group becomes the acetate methyl carbon. The details of the involvement of methylcobalamin in this process are, however, unknown. 

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