This gene encodes an accessory enzyme which participates in the beta-oxidation and metabolism of unsaturated fatty enoyl-CoA esters. 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.