   1.3.1.109 | FAD |
the electron transferring flavoprotein (EtfAf) contains one FAD (alpha-FAD) in subunit alpha and a second FAD (beta-FAD) in subunit beta. butanoyl-CoA dehydrogenase also contains FAD. beta-FAD of the the electron transferring flavoprotein is the acceptor of the hydride of NADH. The formed beta-FADH- is considered as the bifurcating electron donor. As a result of a domain movement, alpha-FAD is able to approach beta-FADH- by about 4 A and to takeup one electron yielding a stable anionic semiquinone, alpha-FAD-/* , which donates this electron further to the FAD of butanoyl-CoA dehydrogenase BcdAf after a second domain movement. The remaining nonstabilized neutral semiquinone, beta-FADH*, immediately reduces ferredoxin. This electron flow from beta-FADH* to ferredoxin is only accomplished if the thermodynamically more favorable electron transfer to alpha-FAD-*. is prevented. Therefore, after the first electron transfer to alpha-FAD, a rotation is postulated of domain II toward the FAD binding site of butanoyl-CoA dehydrogenase BcdAf (based on spectroscopic and structural data). This conformational change, concomitantly, also reduces the distance between alpha-FAD-* and FAD from butanoyl-CoA dehydrogenase from about 30 to about 10 A. Thus, alpha-FAD embedded into the weakly associated domain II serves as a shuttle between the electron-donating beta-FADH- and the electron-accepting FAD of butanoyl-CoA dehydrogenase. Repetition leads to reduction of crotonyl-CoA |
732165 |
