The electron transfer flavoprotein serves as a specific electron acceptor for several dehydrogenases, including five acyl-CoA dehydrogenases, glutaryl-CoA and sarcosine dehydrogenase. It transfers the electrons to the main mitochondrial respiratory chain via ETF-ubiquinone oxidoreductase (ETF dehydrogenase) (By similarity). Involved in leucine catabolism and in phytol degradation. Binds 1 FAD per dimer. Binds 1 AMP per subunit. Heterodimer of an alpha and a beta subunit. Expressed constitutively. Not induced by dark treatment or sucrose starvation. Reduced plant viability on extended exposure to darkness and a reduced reproductive performance under normal growth conditions. Belongs to the ETF beta-subunit/FixA family.