Catalyzes the dehydrogenation of acyl-coenzymes A (acyl-CoAs) to 2-enoyl-CoAs, the first step of the beta-oxidation cycle of fatty acid degradation. Is required for E.coli to utilize dodecanoate or oleate as the sole carbon and energy source for growth. a medium-chain 2,3-saturated fatty acyl-CoA + H(+) + oxidized [electron-transfer flavoprotein] = a medium-chain (2E)-enoyl-CoA + reduced [electron-transfer flavoprotein] a long-chain 2,3-saturated fatty acyl-CoA + H(+) + oxidized [electron-transfer flavoprotein] = a long-chain (2E)-enoyl-CoA + reduced [electron-transfer flavoprotein] Lipid metabolism; fatty acid beta-oxidation. Transcription of fadE is negatively regulated by FadR. Induced in the presence of fatty acids, in a FadR-dependent manner. Cells lacking this gene are unable to grow on octanoate, decanoate, dodecanoate, or oleate as the sole carbon and energy source, but grow well on acetate, while the wild-type strain can grow on acetate, dodecanoate, and oleate. Belongs to the acyl-CoA dehydrogenase family. Was originally named fadF. Truncated N-terminus.