methenyltetrahydromethanopterin

Methenyltetrahydromethanopterin, commonly referred to as methenyl-H4MPT, is a one-carbon carrier cofactor used in the methanogenesis pathway of archaea. It is a derivative of tetrahydromethanopterin (H4MPT), a pterin-based cofactor that participates in transferring single-carbon units during methane production.

In the H4MPT-dependent pathway, carbon dioxide is progressively reduced to methane through a sequence of one-carbon transformations. Formyl-H4MPT is formed first and is then oxidized to methenyl-H4MPT (the methenyl form). This intermediate can be interconverted with other oxidation states of the H4MPT cycle, including methylene-H4MPT and methyl-H4MPT, through a series of enzymatic reactions. The methyl group ultimately ends up transferred to coenzyme M via methyl-H4MPT:CoM methyltransferase (Mtr), enabling downstream steps that yield methane.

The methenyl form of H4MPT plays a central role as an intermediary that carries a one-carbon unit within the cycle. The overall H4MPT system provides a means to shuttle and couple one-carbon conversions to energy conservation in methanogenic metabolism, particularly under anaerobic conditions. Methenyltetrahydromethanopterin is thus a component of a specialized archaeal cofactor network that underpins methane biosynthesis.

Organisms employing this chemistry are predominantly methanogenic archaea. The pathway and its intermediates, including methenyl-H4MPT, reflect a distinctive strategy for carbon processing and energy economy in these organisms.