Fig. 5

The proposed role for each of the two copies of formylmethanofuran dehydrogenase in Methanocorpusculum parvum. Mcor. parvum contains two copies of the formylmethanofuran dehydrogenase complex, one clustered with the Eha energy conserving hydrogenase and one clustered with the heterodisulfide reductase (HdrABC/MvhD) complex. We propose that the two complexes are specific to different ferredoxins, helping to separate the electron pool utilized for anabolism from that utilized to replenish methanogenesis intermediates as previously proposed [49]. The Eha-mediated electron transfer results in no net energy gain through methanogenesis, but replenishes intermediates lost to leaky electron bifurcation or biosynthesis and anabolism. The Hdr mediated electron transfer functions similarly to Class 1 methanogens through electron bifurcation, resulting in a net gain of energy from methanogenesis. Since MvhAG are not present, the best explanation is through use of FrhAG, however that association still needs to be experimentally verified.