ECH1 is a member of the hydratase/isomerase superfamily. ECH1 shows high sequence similarity to enoyl-CoA hydratases of several species, particularly within a conserved domain characteristic of these proteins. ECH1 contains a C-terminal peroxisomal targeting sequence and localizes to peroxisomes. The rat ortholog, which localizes to the matrix of both the peroxisome and mitochondria, can isomerize 3-trans, 5-cis-dienoyl-CoA to 2-trans,4-trans-dienoyl-CoA, indicating that it is a delta3,5-delta2,4-dienoyl-CoA isomerase. ECH1 functions in the auxiliary step of the fatty acid beta-oxidation pathway. Expression of the rat gene is induced by peroxisome proliferators.