Fatty acid ester turnover: a control factor in triacylglycerol and lipid-rich particle accumulation in cultured mammalian cells
Mackenzie, C.G.; Moritz, E.; Wisneski, J.A.; Reiss, O.K.; Mackenzie, J.B.
Molecular and Cellular Biochemistry 19(1): 7-15
ISSN/ISBN: 0300-8177 DOI: 10.1007/bf00231229
Experiments with albumin-bound [1-14C] palmitic acid, in which fatty acid synthesis was repressed, have shown that the larger accumulation of triacylglycerol and lipid-rich particles in a representative high-lipid cell, a rabbit liver cell clone, as compared to a representative low-lipid cell, a HeLa cell clone, was due primarily to the faster turnover of lipid in the HeLa cell. In short-term experiments, the specific activities of the following lipid fractions were twice as high in the HeLa as in the rabbit liver cells: total cell lipid, phospholipid, triacyglycerol and the palmitic acid isolated from the latter fractions. The palmitic acid content of the cell lipid, as well as its oxidation to CO2, was approximately the same in the 2 cell lines. In long-term experiments, the specific activity of the total cell lipid of the rabbit cell approached that of the HeLa cell. Two-thirds of the triacyglycerol palmitic acid in both cell lines was derived from the albumin-bound [1-14C]palmitic acid of the medium. Two-thirds and two-fifths of the phospholipid palmitic acid in the HeLa and rabbit cells, respectively, were derived from this same source. In chase experiments employing these heavily labeled cells, the percent secretion of radioactive lipid, especially fatty acids derived from triacylglycerol, was substantially higher in the HeLa than in the rabbit liver cells. Despite the differences in turnover rates, the results indicate that in both cell lines the fatty acids of the lipid-rich particles were in dynamic equilibrium with the albumin-bound fatty acids of the serum.