NADPH-dependent reductive metabolism of cis-5 unsaturated fatty acids. A revised pathway for the beta-oxidation of oleic acid

Cis-5 double bond in a fatty acid or when encountered through the beta-oxidation of an odd-numbered double-bond unsaturated fatty acid presents as a metabolic block to the further beta-oxidation. Cis-5-fatty acyl-CoA cannot be beta-oxidized to cis-3-enoyl-CoA as suggested by the conventional pathway. Instead, this metabolic block can only be removed through an NADPH-dependent reduction of 5-enoyl-CoA, possibly mediated by a 5-enoyl-CoA reductase. In the case of oleic acid two cycles of beta-oxidation yield cis-5-tetradecenoyl-CoA. This intermediate is then reduced to tetradecanoyl-CoA, which is metabolized further via normal beta-oxidation cycles. The conventional pathway through cis-3-dodecenoyl-CoA does not operate in rat liver.