Unlike the breakdown of saturated fat, cis and trans polyunsaturated fatty acid degradation requires three additional enzymes to generate a product compatible with the standard beta oxidation pathway.Substrate length for mDECR catalysis is thought to be limited at 20 carbons, at which this very long chain fatty acid is first partially oxidized by pDECR in the peroxisome.In the final step, a proton is abstracted from the water[11] to the Cα and the thioester is reformed, resulting in a single Cβ-Cγ trans double bond.[8] 2,4 Dienoyl-CoA Reductase from Escherichia coli shares very similar kinetic properties to that of eukaryotes, but differs significantly in both structure and mechanism.[11] The active site contains accurately positioned Tyr166 that donates a proton to the Cγ after hydride attack at the Cδ, completing the reduction in a single concerted step.[8] The structure of the ternary complex of pDCR (peroxisomal 2,4-dienoyl CoA reductases) with NADP and its substrate provides essential and unique insights into the mechanism of catalysis.
Proposed mechanism of 2,4-Trans dienoyl-CoA reduction by NADPH in mammalian DECR. The mechanism proceeds stepwise through an enolate intermediate.