Positional isomers of unsaturated fatty acids in rat liver lipids

Abstract

The fatty acids of liver lipids from rats raised on a fat free diet from the 30th to the 90th day after birth were analyzed with special regard to the detection of positional isomers of mono-, di-, tri-, and tetraenoic fatty acids. The methyl esters obtained after transesterification of total lipids were separated by argentation chromatography into five fractions: I saturated, II monoenoic, III dienoic, IV dienoic nonmethylene interrupted, V tri- and tetraenoic fatty acid esters. After hydroxylation of the double bonds with osmium tetroxide, the analysis of the poly-O-trimethylsilyl derivatives by gas liquid chromatography on S.C.O.T. columns combined with mass spectrometry revealed the presence of 19 monoenoic, 15 dienoic, and 9 trienoic as well as 3 tetraenoic fatty acid isomers including the normally occurring representatives of the (n-3), (n-6), (n-7), and (n-9) fatty acid families. The majority of the identified isomers can be coordinated to one of these families like 7-16:1; 11-20:1; 6,9-18:2; 8,11-20:2; 5,11-20:2; 5,8,11-20:3; 7,10,13-22:3 to the (n-9) family, 11-18:1; 13-20:1; 5,11-18:2; 7,13-20:2; 6,11-18:2; 6,9-16:2; 8,11-18:2; 10,13-20:2; 5,8,11-18:3; 7,10,13-20:3; 4,7,10,13-20:4 to the (n-7) family and 11,14-20:2; 5,11,14-20:3; 6,9,12-18:3; 8,11,14-20:3; 5,8,11,14-20:4; 7,10,13,16-22:4 to the (n-6) family. All these naturally occuring isomers can be placed into a network of desaturation and chain elongation steps which allows certain conclusions about the substrate specificity of the delta6-, delta5- and delta4-desaturase systems. The great number of isomers found in the (n-7) family indicates that the members of this family are actively metabolized in partial essential fatty acid deficiency.

Nutrition and Biochemistry of Trans and Positional Fatty Acid Isomers in Hydrogenated Oils

“…Nineteen 18: 1 isomers, fifteen 18:2 isomers, and nine 18:3 isomers identified in tissue lipids from rats on a fat-free diet have been reported (182), and other similar data have been published (225,226). Presumably these isomers are formed by desaturation of …”

Structures, practical sources (gymnosperm seeds), gas-liquid chromatographic data (equivalent chain lengths), and mass spectrometric characteristics of all-cis Δ5-olefinic acids

“…However, if these data are known, both kinds of calculation should lead to the same result. For example, the theoretical ECL of 5,9,12-C18:3 acid is: ECL (5,9-C18:2) + ECL (9,12-C18:2) -ECL (9 e These acids were reported to occur in small amounts in rat lipids (see, e.g., [72]). confused with 5,11,14-C20:3 acid (ECL = 20.83).…”

Separation of 20∶4n−6 and 20∶4n−7 by capillary gas‐liquid chromatography

“…2a and b). All these eicosadienoic acids were previously identified in the liver lipids of rats fed a fat-free diet (11).…”

“…Several investigators (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) have observed that fatdeficient diets can lead to the appearance of polyunsaturated fatty acids of the n-7 series in phospholipids. These acids include 18:2A8,11 (4,5,7,8,11), 18:3A5,8,11 (2,8,11), 20:2A10,13 Ill), 20:3A7,10,13 (1,(4)(5)(6)(7)(8)10,11) and 20:4A4,7,10,13 (3-9,11) acids. Unfortunately, these acids are usually not well resolved from similar fatty acids by gas-liquid chromatography (GLC) on packed columns (6,7,9,12,13}.…”