Auxiliary enzyme of beta-oxidation. It participates in the metabolism of unsaturated fatty enoyl-CoA esters having double bonds in both even- and odd-numbered positions. Catalyzes the NADP-dependent reduction of 2,4-dienoyl-CoA to yield trans-3-enoyl-CoA (By similarity). a 4,5-saturated-(2E)-enoyl-CoA + NADP(+) = a (2E,4E)-dienoyl-CoA + H(+) + NADPH a (2E,4Z)-dienoyl-CoA + H(+) + NADPH = a 4,5-saturated-(2E)-enoyl-CoA + NADP(+) Lipid metabolism; fatty acid beta-oxidation. Repressed by FadR in the absence of LCFAs (fatty acids of 14-20 carbon atoms). When LCFAs are present in the medium, they are converted to long-chain acyl-CoAs, which antagonize FadR as to its binding to fadR boxes on target DNA and thus derepress transcription. Belongs to the short-chain dehydrogenases/reductases (SDR) family. 2,4-dienoyl-CoA reductase subfamily.