Coenzyme-B sulfoethylthiotransferase

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coenzyme-B sulfoethylthiotransferase
EC number
IntEnz IntEnz view
ExPASy NiceZyme view
MetaCyc metabolic pathway
PRIAM profile
PDB structures RCSB PDB PDBe PDBsum
Gene Ontology AmiGO / EGO

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 donor coenzyme 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)[1][2] that encode and express the set of genes of this enzymatic complex.

The enzyme has two active sites, each occupied by the nickel-containing F430 cofactor.[3]

2-(methylthio)ethanesulfonate (methyl-CoM) + N-(7-mercaptoheptanoyl)threonine 3-O-phosphate (coenzyme B) \rightleftharpoons CoM-S-S-CoB + methane

Thus, the two substrates of this enzyme are 2-(methylthio)ethanesulfonate and N-(7-mercaptoheptanoyl)threonine 3-O-phosphate, whereas its two products are CoM-S-S-CoB and methane.

In some species, the enzyme reacts in reverse (a process called reverse methanogenesis), catalysing the anaerobic oxidation of methane, therefore removing it from the environment.[4] Such organisms are methanotrophs.

This enzyme belongs to the family of transferases, specifically those transferring alkylthio groups.

This enzyme participates in folate biosynthesis.[citation needed]


coenzyme-B sulfoethylthiotransferase is a protein complex made up of a pair of identical halves. Each half up of 3 subunits: α, β and γ,[5] also called McrA, McrB and McrG, respectively.


  1. ^
  2. ^ Whitford, M. F.; Teather, R. M.; Forster, R. J. (2001). "Phylogenetic analysis of methanogens from the bovine rumen". BMC microbiology 1: 5. PMC 32158. PMID 11384509.  edit
  3. ^ Thauer, R. K., "Biochemistry of methanogenesis: a tribute to Marjory Stephenson", Microbiology, 1998, 144, 2377-2406. doi:10.1099/00221287-144-9-2377 PMID 9782487
  4. ^ Hallam, S. J.; Putnam, N.; Preston, C. M.; Detter, J. C.; Rokhsar, D.; Richardson, P. M.; Delong, E. F. (2004). "Reverse Methanogenesis: Testing the Hypothesis with Environmental Genomics". Science 305 (5689): 1457–1462. doi:10.1126/science.1100025. PMID 15353801.  edit
  5. ^ Ermler, U.; Grabarse, W.; Shima, S.; Goubeaud, M.; Thauer, R. K. (1997). "Crystal structure of methyl-coenzyme M reductase: The key enzyme of biological methane formation". Science 278 (5342): 1457–1462. doi:10.1126/science.278.5342.1457. PMID 9367957.  edit

Further reading[edit]

  • Bobik TA, Olson KD, Noll KM, Wolfe RS (1987). "Evidence that the heterodisulfide of coenzyme M and 7-mercaptoheptanoylthreonine phosphate is a product of the methylreductase reaction in Methanobacterium". Biochem. Biophys. Res. Commun. 149 (2): 455–60. doi:10.1016/0006-291X(87)90389-5. PMID 3122735. 
  • Ellermann J, Hedderich R, Boecher R and Thauer RK (1988). "The final step in methane formation: investigations with highly purified methyl coenzyme M reductase component C from Methanobacterium thermoautotrophicum (strain Marburg)". Eur. J. Biochem. 184 (1): 63–68. doi:10.1111/j.1432-1033.1989.tb14990.x. PMID 2506016. 
  • Signor L, Knuppe C, Hug R, Schweizer B, Pfaltz A, Jaun B (2000). "Methane formation by reaction of a methyl thioether with a photo-excited nickel thiolate--a process mimicking methanogenesis in archaea". Chemistry. 6 (19): 3508–16. doi:10.1002/1521-3765(20001002)6:19<3508::AID-CHEM3508>3.3.CO;2-N. PMID 11072815.