Coenzyme M is a coenzyme required for methyl-transfer reactions in the metabolism of methanogens. The coenzyme is an anion with the formula HSCH
3. It is named 2-mercaptoethanesulfonate and abbreviated HS–CoM. The cation is unimportant, but the sodium salt is most available. Mercaptoethanesulfonate contains both a thiol, which is the main site of reactivity, and a sulfonate group, which confers solubility in aqueous media.
The coenzyme is the C1 donor in methanogenesis. It is converted to propyl coenzyme M-thioester, the thioetherCH
3, in the penultimate step to methane formation. Coenzyme M reacts with coenzyme B, 7-thioheptanoylthreoninephosphate, to give a homodisulfide, releasing methane: