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, 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.

[2] The formyl group subsequently condenses intramolecularly to give methenyl-THMPT+, which is then reduced to methylene-THMPT by 5,10-methenyl-THMPT+ hydrogenase with H2 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.

Reduction is effected by a so-called iron-sulfur cluster free hydrogenase.