Positional distribution of exogenous and endogenous fatty acids in triacylglycerols formed by rat adipocytes in vitro.

Rat adipocytes were used in vitro to compare the positional distributions of fatty acids of intra- and extra-cellular origin in triacyl-sn-glycerols. Fatty acids of extracellular origin were esterified to each position in similar, but not identical, proportions to the natural distributions. A high proportion of the oleic acid synthesised in the tissue by desaturation of exogenous stearic acid was found in position sn-3. When palmitic acid was the only fatty acid added, tripalmitoylglycerol was synthesised by the adipocytes. The rate and pattern of fatty acids synthesised de novo from acetate was dependent on the age of the donor rat and the concentration of acetate and presence or absence of long-chain fatty acids in the medium. The newly synthesised fatty acids were esterified in very different proportions from the natural distributions and thus from those of extracellular fatty acids. The results are discussed in terms of esterification of the fatty acids from the two sources in different compartments of the cell.