Evidence for a structurally specific role of essential polyunsaturated fatty acids depending on their peculiar double-bond distribution in biomembranes.

ESR spectrometry with 5-, 7-, 10-, and 12-doxylstearate probes and a combined index considering separately the double-bond numbers of essential and nonessential fatty acids were used to investigate the structural role of the double bonds of polyunsaturated fatty esters in membrane phosphoglycerides. Purified brush border membrane vesicles were prepared from the jejunum of piglets receiving either high (HLA) or low (LLA) dietary levels of linoleic acid (18:2 n-6). In the LLA as compared to the HLA group, there were no significant modifications of (a) the relative contents of cholesterol, phospholipid, and protein and of (b) the phosphoglyceride class distribution, contrasting with very large changes in the fatty acid compositions of each phosphoglyceride. These changes were characterized by an increase in nonessential monoene and triene (18:1 n-9 and 20:3 n-9) and a decrease in essential diene (18:2 n-6) in LLA- as compared to HLA-fed piglets. The essential tetraene 20:4 n-6 remained rather constant despite an overall nonsignificant increase in the LLA group. The total double-bond number (TDBn) was not significantly affected, contrasting with the variations in the double-bond numbers of essential and nonessential fatty acids (DBn(EFA) and DBn(nonEFA), respectively). The combined DBn(EFA)/DBn(nonEFA) index was 1.7-3.3 times lower in LLA than in HLA membrane phospholipids. It was concluded that the diet was able to affect the double-bond distribution in the upper and inner half-parts of the membrane leaflet without changing the total number of double bonds.(ABSTRACT TRUNCATED AT 250 WORDS)