Tetrahydromethanopterin (THMPT)

Tetrahydromethanopterinis a coenzyme in methanogenesis. It is the carrier of the C1 group as it is reduced to the methyl level, before transferring to the coenzyme M.Tetrahydrosarcinapterin (THSPT, H₄SPT) is a modified form of THMPT, wherein a glutamyl group linked to the 2-hydroxyglutaric acid terminus.

N-Formylmethanofuran donates the C1 group to the N5 site of the pterin to give the formyl- THMPT. The formyl group subsequently condenses intramolecularly to give methenyl- THMPT⁺, which is then reduced to methylene- THMPT. Methylene- MPT is subsequently converted, using coenzyme F420 as the electron source, to methyl- THMPT, catalyzed by F₄₂₀-dependent methylene- THMPT reductase. Methyl- THMPT is the methyl donor to coenzyme M, a conversion mediated by methyl- THMPT:coenzyme M methyl-transferase.