Coenzyme-B sulfoethylthiotransferase

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.

Ruminants (e.g. cows) produce methane because their rumens contain methanogenic prokaryotes (Archaea)[2][3] that encode and express the set of genes of this enzymatic complex.

[4] The two substrates of this enzyme are 2-(methylthio)ethanesulfonate and N-(7-mercaptoheptanoyl)threonine 3-O-phosphate; its two products are CoM-S-S-CoB and methane.

Coenzyme-B sulfoethylthiotransferase is a multiprotein complex made up of a pair of identical halves.

Each half is made up of three subunits: α, β and γ,[7] also called McrA, McrB and McrG, respectively.