FIG 3.

The aceticlastic pathway of methanogenesis for M. barkeri. Acetate is first converted to acetyl-CoA in an ATP-dependent manner (not shown), which is then split by acetyl-CoA decarbonylase/synthase (ACDS) into an enzyme-bound carbonyl ([CO]) and a methyl group, which gets transferred to the C₁ carrier tetrahydrosarcinapterin. Oxidation of [CO] to CO₂ produces reduced ferredoxin (Fd_red), which is oxidized by Ech, thereby generating H₂ inside the cell. H₂ diffuses across the cell membrane to the Vht active site, where it is oxidized and electrons are used to reduce methanophenazine (MP_red). Reduction of the methyl group bound to coenzyme M by coenzyme B produces CH₄ and a disulfide of CoM and CoB, which is regenerated by reduction with electrons from MP_red via the heterodisulfide reductase enzyme. Portions of the methanogenic pathway that are not required for aceticlastic methanogenesis, including the use of Frh, are shown in light gray.