Fig. 1.

Reaction of the EtfAB/Bcd complex. In the first round the EtfAB/Bcd complex catalyzes the NADH-dependent reduction of β-FAD to β-FADH⁻, which bifurcates. One electron reduces α-FAD•⁻ to α-FADH⁻ and the other ferredoxin to ferredoxin⁻. α-FADH⁻ swings to δ-FAD forming δ-FADH• and α-FAD•⁻, which returns to β-FAD. The second round generates a second ferredoxin⁻ and δ-FADH⁻, which reduces crotonyl-CoA to butyryl-CoA