Tetrahydromethanopterin
Tetrahydromethanopterin (THMPT, Template:Chem/link) is 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.[1]
Tetrahydrosarcinapterin (THSPT, Template:Chem/link) is a modified form of THMPT, wherein a glutamyl group linked to the 2-hydroxyglutaric acid terminus.
THMPT is the main platform for C1 transformations
N-Formylmethanofuran donates the C1 group to the N5 site of the pterin to give the formyl- THMPT.[2] The formyl group subsequently condenses intramolecularly to give methenyl-Template:Chem/link, which is then reduced to methylene-THMPT by [[5,10-Methenyltetrahydromethanopterin hydrogenase|5,10-methenyl-Template:Chem/link hydrogenase]] with Template:Chem/link as the electron donor.[3] 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 methyltransferase.[1]
Comparison with tetrahydrofolic acid
THMPT is related to the better known tetrahydrofolic acid (THFA, Template:Chem/link). The most important difference between THMPT and THFA is that THFA has an electron-withdrawing carbonyl group on the phenyl ring. As a consequence, methenyl- THMPT is more difficult to reduce than methenyl- THFA. Reduction is effected by a so-called iron-sulfur cluster free hydrogenase.[3] The cumbersome name distinguishes this hydrogenase from the so-called Fe-only hydrogenases that do contain Fe-S cluster.
References
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