In enzymology, coenzyme-B sulfoethylthiotransferase, also known as methyl-coenzyme M reductase (MCR) or most systematically as 2-(methylthio)ethanesulfonate:N-(7-thioheptanoyl)-3-O-phosphothreonine S-(2-sulfoethyl)thiotransferase is an enzyme that catalyzes the final step in the formation of methane. It does so by combining the hydrogen donorcoenzyme B and the methyl donor coenzyme M. Via this enzyme, most of the natural gas on earth was produced. Ruminants (e.g. cows) produce methane because their rumens contain methanogenic prokaryotes (Archaea) that encode and express the set of genes of this enzymatic complex.
In some species, the enzyme reacts in reverse (a process called reverse methanogenesis), catalysing the anaerobicoxidation of methane, therefore removing it from the environment. Such organisms are methanotrophs.
This enzyme belongs to the family of transferases, specifically those transferring alkylthio groups.
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