Heterodimeric electron transfer flavoprotein that accepts electrons from several mitochondrial dehydrogenases, including acyl-CoA dehydrogenases, glutaryl-CoA and sarcosine dehydrogenase (PubMed:25416781, PubMed:15159392, PubMed:15975918). It transfers the electrons to the main mitochondrial respiratory chain via ETF-ubiquinone oxidoreductase (Probable). Required for normal mitochondrial fatty acid oxidation and normal amino acid metabolism (PubMed:12815589, PubMed:7912128). ETFB binds an AMP molecule that probably has a purely structural role (PubMed:8962055, PubMed:15159392, PubMed:15975918). Heterodimer composed of ETFA and ETFB (PubMed:25023281, PubMed:25416781, PubMed:8962055, PubMed:15159392, PubMed:15975918). Identified in a complex that contains ETFA, ETFB and ETFRF1 (PubMed:27499296). Interacts with ACADM (PubMed:15159392, PubMed:15975918). Abundant in liver, heart and skeletal muscle. A weak expression is seen in the brain, placenta, lung, kidney and pancreas. The recognition loop recognizes a hydrophobic patch at the surface of interacting dehydrogenases and acts as a static anchor at the interface. Methylated. Trimethylation at Lys-200 and Lys-203 may negatively regulate the activity in electron transfer from acyl-CoA dehydrogenases. The disease is caused by variants affecting the gene represented in this entry. Belongs to the ETF beta-subunit/FixA family.