Fig. 3.
Model of complex of proteins that interact with Hdr. When H2 is used as the electron donor for methanogenesis, electrons are transferred to Hdr via Vhu. Flavin-mediated electron bifurcation at HdrA then results in reduction of the CoM-S-S-CoB heterodisulfide and a ferredoxin that is used by Fwd for the first step in methanogenesis. When hydrogen is limiting or is replaced by formate, Fdh is highly expressed (10) and incorporates into the complex. When formate is used as the electron donor for methanogenesis, electrons are transferred to Hdr from formate via Fdh. Fd(red), reduced ferredoxin; Fd(ox), oxidized ferredoxin.