Contains FAD. The reaction is catalysed in the opposite direction to that shown. The enzyme from the bacterium Clostridium propionicum is a complex that includes an electron-transfer flavoprotein (ETF). The ETF is reduced by NADH and transfers the electrons to the active site. Catalyses a step in a pathway for L-alanine fermentation to propanoate . cf. EC 18.104.22.168, acrylyl-CoA reductase (NADPH).