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Short-Term Effects of Free Fatty Acids on the Regulation of Fatty Acid Biosynthesis in Ehrlich Ascites Tumor Cells

Departments of Biochemistry [RM, AS] and Internal Medicine [AS], University of Iowa, Iowa City, Iowa 52242

Fatty acid biosynthesis in Ehrlich ascites tumor cells was studied in vitro by measuring the incorporation of ³H₂O into saponifiable lipids. Glucose was found to be a much better substrate for fatty acid synthesis than acetate, ß-hydroxybutyrate, or amino acids. Enzyme assays using Ehrlich cell cytosol preparations demonstrated the presence of the de novo biosynthetic enzymes, acetyl coenzyme A carboxylase and fatty acid synthetase. The distribution of ³H between various fatty acids separated using gas-liquid chromatography suggested, however, that both de novo synthesis and chain elongation occur in intact Ehrlich cells. The existence of an elongation pathway was confirmed by demonstrating that considerable amounts of radioactivity were present in fatty acids longer than palmitate when cells were incubated with palmitate-1-¹⁴C. Total fatty acid synthesis was inhibited when stearate, palmitate, oleate, or linoleate was added to incubation media containing bovine serum albumin. Stearate produced the largest effect, as much as 85% inhibition under certain conditions. By contrast, myristate had little effect on and laurate actually stimulated total fatty acid synthesis. In agreement with these observations, both laurate and lauroyl coenzyme A stimulated acetyl coenzyme A carboxylase in an Ehrlich cell homogenate, while stearate and stearoyl coenzyme A inhibited the enzyme. These findings indicate that, as in nonmalignant cells, fatty acid synthesis in the Ehrlich cell is subject to short-term regulation by extracellular free fatty acids.

Received 5/ 6/74. Accepted 9/ 9/74.