Probable catalytic subunit of the acryloyl-CoA reductase complex involved in the pathway of L-alanine fermentation. Catalyzes the irreversible NADH-dependent formation of propionyl-CoA from acryloyl-CoA. It can also use 3-buten-2-one as substrate. NAD(+) + propanoyl-CoA = acryloyl-CoA + H(+) + NADH kcat is 4.5 sec(-1), 29 sec(-1), 2 sec(-1) and 3.5 sec(-1) for acryloyl-CoA, 3-buten-2-one, propionyl-CoA and butyryl-CoA, respectively (at pH 7.5 and 25 degrees Celsius). Optimum pH is between 6.5 and 7. In the range between 25 and 55 degrees Celsius, the activity increases with rising temperature. Above 55 degrees Celsius, it decreases and becomes almost zero at 65 degrees Celsius. Heterohexadecamer; tetramer of tetramers. Each tetramer is composed of 2 alpha (AcrC), a beta (AcrA) and a gamma (AcrB) subunit. Belongs to the acyl-CoA dehydrogenase family.