Fig 8.

Model of caffeate respiration in A. woodii. The electron flow from molecular hydrogen to caffeate is shown. Ferredoxin is reduced by a bifurcating hydrogenase and reoxidized by the Rnf complex, which generates a sodium ion gradient across the cytoplasmic membrane. NADH serves as an electron donor for the caffeyl-CoA reducing complex, potentially encoded by carCDE, which might reduce another ferredoxin via electron bifurcation, fueling the Rnf complex. Caffeate is initially activated by CarB (A), whereas CarA catalyzes an energy-saving CoA loop in the steady state of caffeate respiration (B).