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). 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.