Inhibition of fatty acid Δ6- andΔ5-desaturation by cyclopropene fatty acids in rat liver microsomes

Abstract

Δ 6-Desaturation of linoleic acid and Δ 5-desaturation of dihomo-γ-linolenic acid were measured in liver microsomes from ra fresh Baobab seed oil containing cyclopropene fatty acids (malvalic acid and sterculic acid) or heated Baobab seed oil practically devoid of these fatty acids or control oil. The presence of cyclopropene fatty acids in the fresh Baobab oil diet highly depressed both desaturations, but Δ6- more than Δ 5-desaturation. The decreased capacity of microsomes to desaturate was reflected in the lower arachidonic acid content in microsomal phospholipids from rats fed this oil. However it was also lower in rats fed heated oil although in vitro Δ 6- and Δ 5-desaturation were not depressed. When liver microsomes prepared from rats fed the control diet were used for the desaturation assays, the presence of free malvalic or sterculic acid in the medium, also highly depressed Δ 6- and Δ 5-desaturation. The incorporation of arachidonic acid, the product of Δ 5-desaturation, into phospholipids was also highly depressed, while that of the precursor dihomo-γ-linolenic acid was not. This suggests that cyclopropene fatty acids specifically inhibit incorporation of the Δ 5-desaturation product into phospholipids or that they specifically inhibit desaturation of the substrate previously incorporated into a membrane phospholipid.