Abstract
The function of the two FADs of electron-transferring flavoprotein (ETF) from the anaerobic bacterium Megasphaera elsdenii was investigated. ETF is known to receive electrons from NADH and D-lactate dehydrogenase (LDH) and donate the electrons to butyryl-CoA dehydrogenase. In this study, reactions of ETF with NADH and LDH were analyzed. During NADH titration of ETF, one FAD (named FAD-I) was first reduced in one-electron manner, and the other FAD (FAD-II) was then reduced in two-electron manner. Direct one-electron transfer from NADH to FAD-I is unlikely because NADH is known to be a two-electron reductant. The reduction of FAD-I in one-electron manner can be explained by electron transfer between ETF molecules. This is because the electron transfer from reduced FAD-II to oxidized FAD-I was observed when reduced ETF was mixed with oxidized ETF. LDH reduced only FAD-I in the presence of D-lactate, showing that LDH interacts with FAD-I but not with FAD-II. Fully reduced ETF, where both FAD-I and FAD-II were reduced with NADH, was oxidized by LDH in the presence of pyruvate, resulting in the oxidation of both FAD-I and FAD-II. Kinetic analysis of this reaction revealed that LDH receives electrons from only FAD-I, and the oxidized FAD-I receives electrons from FAD-II. [Jpn J Physiol 55 Suppl:S79 (2005)]
