Methanogens central metabolism

Experimental studies of Methanosarcina and current understanding of the organism s metabolic pathway allow us to estimate the parameters in the thermodynamic term (Qusheng Jin, personal communication). The methanogens conserve about 24 kJ (mol acetate)-1, so we set AGp to 48 kJ mol-1 and m to one half. A double proton translocation occurs within the central metabolic pathway, furthermore, so, if we take these as the rate limiting steps, the average stoichiometric number / is two. 

The tetrapyrrole-type coenzyme F430 (19) was named on basis of its absorption maximum at 430 mn. The nickel-chelating factor is biosynthesized via the porphyrin biosynthetic pathway (Fig. 2) (19). For the handling of one-carbon fragments that play a central role in their metabolism, methanogenic bacteria use methanopterin (34, Fig. 3). The tetrahydropterine system that serves as the business end of the methanopterin coenzyme family is structurally similar to tetrahydrofolate, and the biosynthetic pathway starting from GTP is similar to that of tetrahydrofolate (Fig. 3). The ribitylaniline moiety is derived from ribose and from the shikimate pathway via 4-amino-benzoate (55). 

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