Acryloyl-CoA reductase fromClostridium propionicum catalyses the irreversible NADH-dependent formation of propionyl-CoA from acryloyl-CoA. Purification yielded a heterohexadecameric yellow–greenish enzyme complex [(a2bc)4; molecular mass 600 ± 50 kDa] composed of a propionyl-CoA dehydrogenase (a2,2·40 kDa) and an electron-transferring flavoprotein (ETF; b,38kDa;c, 29 kDa). A flavin content (90% FAD and 10% FMN) of mol pera2bcsubcomplex (149 kDa) was determined.