Enoyl-CoA-(∆) isomerase (, also known as dodecenoyl-CoA-(∆) isomerase, 3,2-trans-enoyl-CoA isomerase, ∆3(cis),∆2(trans)-enoyl-CoA isomerase, or acetylene-allene isomerase, is an enzyme that catalyzes the conversion of cis- or trans-double bonds of coenzyme A (CoA) bound fatty acids at gamma-carbon (position 3) to trans double bonds at beta-carbon (position 2) as below: This enzyme has an important role in the metabolism of unsaturated fatty acids in beta oxidation. Mechanism Enoyl-CoA isomerase is involved in the beta-oxidation, one of the most frequently used pathways in fatty acid degradation, of unsaturated fatty acids with double bonds at odd-numbered carbon positions. It does so by shifting the position of the double bonds in the acyl-CoA intermediates and converting 3-cis or trans-enoyl-CoA to 2-trans-enoyl-CoA. Since the key step in the degradation of fatty acids with double bonds at even-numbered carbon positions also produces 3-trans-enoyl-CoA in mammals and yeasts, enoyl-CoA isomerase is technically required for their metabolism as well. The reaction mechanism is detailed in figure 1, and the base that initiates the isomerization and NH groups that stabilize the intermediate are located on the active site of enoyl-coA isomerase. As it functions in the step immediately preceding the actual beta-oxidation and forms a double bond extending from the beta-carbon (position 2), enoyl-CoA isomerase is involved in both the NADPH-dependent and NADPH-independent pathways of beta-oxidation. The double bond serves as the target of oxidation and carbon-to-carbon bond cleavage, thereby shortening the fatty acid chain. Sub-classification Enoyl-CoA isomerases can be categorized into three classes: monofunctional mitochondrial monofunctional peroxisomal multifunctional The monofunctional mitochondrial and peroxisomal enzymes are found in the mitochondria and peroxisomes of eukaryotes, respectively. The multifunctional enzymes are found in bacteria and in the peroxisomes of some eukaryotes, but they serve two functions: the N-terminal domain works the same as the other classes of enoyl-CoA isomerases and the C-terminal domain works as a dehydrogenase, specifically, to 3-hydroxyactyl-CoA. There are two divisions among the mitochondrial enoyl Co-A isomerase: short-chain and long-chain [4]. In an immunoblot, antibodies were run against all enoyl CoA isomerase. However, two of these isomerases had antibody attachment: the short chain isomerase and the peroxisomal multifunctional enzyme. There was one enzyme which did not have binding specificity to this antibody: mitochondrial long-chain isomerase. Long-chain isomerase was found when it eluted at a lower potassium phosphate concentration in the gradient. Thus, the discovery of three sub-classes of enoyl CoA isomerase was made. Although all three classes of enzymes