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Metabolism of Phospholipids in Ehrlich Ascites Tumor¹

Department of Biochemistry, University of Western Ontario, London, Canada

When Ehrlich ascites cells were incubated in a suitable medium containing one of a number of ¹⁴C-labeled phospholipid precursors, radioactivity was recovered from the lipid fraction. For the same concentration and specific radioactivity of precursor, the incorporation was in the following order: choline-1,2-¹⁴C > ethanolamine-1,2-¹⁴C > L-serine-¹⁴C > glycerol-1-¹⁴C > formate-¹⁴C > acetate-1-¹⁴C.

Radioactivity from choline-1,2-¹⁴C was incorporated into the 3 choline-containing phospholipids—lecithin, choline plasmalogen, and sphingomyelin. Radioactivity from ethanolamine-1,2-¹⁴C was incorporated into phosphatidyl ethanolamine, ethanolamine plasmalogen, choline plasmalogen, and lecithin. Radioactivity from L-serine-¹⁴C was incorporated into phosphatidyl serine, serine plasmalogen, and sphingomyelin, and also into phosphatidic acid and other glycerophosphatides. Radioactivity from glycerol-1-¹⁴C was incorporated into phosphatidic acid and the glycerophosphatides, and also into sphingomyelin. Radioactivity from formate-¹⁴C was incorporated into phosphatidyl serine, serine plasmalogen and sphingomyelin, with lesser amounts into other phosphatides. With acetate-1-¹⁴C, radioactivity was poorly incorporated into the phosphatides of this tissue.

These results are discussed in relation to current knowledge concerning the biosynthesis of phosphatides. Evidence is given to support the following generalizations concerning the metabolism of phospholipids in the Ehrlich ascites tumor: (a) The cytosine nucleotide pathway for the biosynthesis of glycerophosphatides is operative. (b) Lipid ethanolamine is methylated to form lipid choline. (c) Phosphatidyl serine is not decarboxylated to yield phosphatidyl ethanolamine.

¹ This investigation was supported by grants from the National Cancer Institute and Medical Research Council of Canada.

² Fellow, National Cancer Institute of Canada.

Received 2/26/65. Revised 6/ 6/65.