Involved in the aerobic and anaerobic degradation of long-chain fatty acids via beta-oxidation cycle. Catalyzes the formation of 3-oxoacyl-CoA from enoyl-CoA via L-3-hydroxyacyl-CoA. It can also use D-3-hydroxyacyl-CoA and cis-3-enoyl-CoA as substrate. a (3S)-3-hydroxyacyl-CoA + NAD(+) = a 3-oxoacyl-CoA + H(+) + NADH a (3S)-3-hydroxyacyl-CoA = a (2E)-enoyl-CoA + H2O a 4-saturated-(3S)-3-hydroxyacyl-CoA = a (3E)-enoyl-CoA + H2O (3S)-3-hydroxybutanoyl-CoA = (3R)-3-hydroxybutanoyl-CoA a (3Z)-enoyl-CoA = a 4-saturated (2E)-enoyl-CoA a (3E)-enoyl-CoA = a 4-saturated (2E)-enoyl-CoA Lipid metabolism; fatty acid beta-oxidation. Heterotetramer of two alpha chains (FadB) and two beta chains (FadA). Repressed by FadR in the absence of LCFAs (fatty acids of, at least, 12 carbon atoms). When LCFAs are present in the medium, they are converted to long-chain acyl-CoAs which bind to FadR resulting in its release from the DNA and thus derepression of the transcription. In the N-terminal section; belongs to the enoyl-CoA hydratase/isomerase family. In the C-terminal section; belongs to the 3-hydroxyacyl-CoA dehydrogenase family.