Able to isomerize both 3-cis and 3-trans double bonds into the 2-trans form in a range of enoyl-CoA species. Essential for the beta oxidation of unsaturated fatty acids (PubMed:18657232). Involved with IBR1 and IBR3 in the peroxisomal beta-oxidation of indole-3-butyric acid (IBA) to form indole-3-acetic acid (IAA), a biologically active auxin (PubMed:20562230). 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. Defective in root hair expansion (PubMed:20562230). Mutant plants are resistant to the inhibitory effect of intermediate levels of indole-3-butyric acid (IBA) and 2,4-DB on root elongation (PubMed:18725356). Belongs to the enoyl-CoA hydratase/isomerase family.