The metabolism of polyenoic fatty acids

Feeding experiments with C¹⁴-labeled and unlabeled unsaturated fatty acids have been used to study the possible routes of formation of the C₂₀- and C₂₂-polyenoic fatty acids of rat liver phosphatides. The acids of the palmitoleate, oleate, linoleate, and linolenate types (considered on the basis of the position of the double bond closest to the methyl end) are apparently formed from the C₁₆ and C₁₈ unsaturated acids of the corresponding types. The results rule out possible transformations of the C₂₀- and C₂₂-polyenoic acids from one type to another, and demonstrate the exclusive introduction of new double bonds toward the carboxyl group. Isomers of linoleate or linolenate in which the double bonds were shifted by one carbon atom toward the carboxyl or methyl groups were incorporated into the phosphatides only to a negligible extent in the form of polyenoic acids.