INHIBITION OF FATTY-ACID DELTA-6-DESATURATION AND DELTA-5-DESATURATION BY CYCLOPROPENE FATTY-ACIDS IN RAT-LIVER MICROSOMES

Delta(6)-Desaturation of linoleic acid and Delta(5)-desaturation of di homo-gamma-linolenic acid were measured in liver microsomes from rats fed fresh Baobab seed oil containing cyclopropene fatty acids (malvali c acid and sterculic acid) or heated Baobab seed oil practically devoi d of these fatty acids or control oil. The presence of cyclopropene fa tty acids in the fresh Baobab oil diet highly depressed both desaturat ions, but Delta 6- more than Delta(5)-desaturation. The decreased capa city of microsomes to desaturate was reflected in the lower arachidoni c acid content in microsomal phospholipids from rats fed this oil. How ever it was also lower in rats fed heated oil although in vitro Delta( 6)- and Delta(5)-desaturation were not depressed. When liver microsome s prepared from rats fed the control diet were used for the desaturati on assays, the presence of free malvalic or sterculic acid in the medi um, also highly depressed Delta(6)- and Delta(5)-desaturation. The inc orporation of arachidonic acid, the product of Delta(5)-desaturation, into phospholipids was also highly depressed, while that of the precur sor dihomo-gamma-linolenic acid was not. This suggests that cycloprope ne fatty acids specifically inhibit incorporation of the Delta(5)-desa turation product into phospholipids or that they specifically inhibit desaturation of the substrate previously incorporated into a membrane phospholipid.