enoylCoA

Enoyl-CoA is a thioester of coenzyme A with an enoyl group, representing a carbon–carbon double bond adjacent to the carbonyl of the acyl unit. In fatty acid catabolism, the most common enoyl-CoA species is trans-Δ2-enoyl-CoA, formed when a fatty acyl-CoA is oxidized by acyl-CoA dehydrogenases to introduce a double bond between the alpha and beta carbons of the acyl chain.

In the beta-oxidation cycle, fatty acids are first activated to fatty acyl-CoA. The initial oxidation by acyl-CoA dehydrogenase yields trans-Δ2-enoyl-CoA, which is then hydrated by enoyl-CoA hydratase to produce 3-hydroxyacyl-CoA. This is subsequently oxidized to 3-ketoacyl-CoA and cleaved to generate acetyl-CoA and a shortened acyl-CoA, continuing the cycle to extract energy as ATP through the mitochondrial or peroxisomal pathways.

Handling of unsaturated fatty acids involves additional enzymes. For substrates with cis double bonds, enoyl-CoA isomerase can convert cis-Δ3-enoyl-CoA into the trans-Δ2-enoyl-CoA form so beta-oxidation can proceed. In some cases, other isomerization steps or auxiliary enzymes may be required, depending on chain length and degree of unsaturation.

Physiological significance includes energy production from fatty acids and the maintenance of lipid homeostasis. Defects in enzymes acting on enoyl-CoA intermediates, such as acyl-CoA dehydrogenases, can lead to metabolic disorders, including impaired fatty acid oxidation and related clinical symptoms.