Heterodimeric electron transfer flavoprotein that accepts electrons from trimethylamine dehydrogenase (PubMed:7798207). It transfers the electrons to the main respiratory chain via ETF-ubiquinone oxidoreductase (ETF dehydrogenase) (Probable). Binds 1 FAD per dimer. Heterodimer of an alpha and a beta subunit. Belongs to the ETF alpha-subunit/FixB family.