THE SELECTIVE MOBILIZATION OF FATTY-ACIDS IS NOT BASED ON THEIR POSITIONAL DISTRIBUTION IN WHITE-FAT-CELL TRIACYLGLYCEROLS

Fatty acids have been shown to be selectively mobilized from rat white fat cells, whatever the dietary manipulations. For convenience, fatty acids have been classified as being highly, weakly and moderately mob ilizable. The aim of this study was to examine whether the selective m obilization of fatty acids can be explained, even partly, by their pos itional distribution in adipose-tissue triacylglycerols (TAG) via the known specificity of hormone-sensitive lipase for the sn-1 and sn-3 po sitions. Adipose tissue was dietarily manipulated in order to obtain a wide spectrum of fatty acids, including large amounts of either very- long-chain polyunsaturated fatty acids (VLC-PUFA) or very-long-chain m onounsaturated fatty acids (VLC-MUFA). The determination of fatty acid distribution in adipose tissue, TAG was based on random formation of 1,2-diacyl-rac-glycerols by Grignard degradation, followed by synthesi s of phosphatidic acids and hydrolysis in the sn-2 position by phospho lipase A(2). Regardless of the fatty acid composition and location of fat depots, highly (e.g. 18:4n-3 and some of the VLC-PUFA) and weakly (e.g. VLC-MUFA) mobilizable fatty acids were located mainly in the out er (sn-1 and sn-3) positions of the glycerol moiety (79.5% and 92.5% o n average, respectively). Other fatty acids, which are rather moderate ly mobilizable, were more randomly distributed. We conclude that the s elective mobilization of white-fat-cell fatty acids is not based on th eir positional distribution in TAG.