Incorporation of choline and ethanolamine into phospholipids in germinating soya bean

1. Incorporation of [Me-14C]choline and [2-14C]ethanolamine into lipids was studied in germinating soya bean (Glycine max L.) seeds. The precursors are only incorporated into phosphatidylcholine and into phosphatidylethanolamine respectively. 2. Base-labelling via a phospholipase-D type of reaction was eliminated as a significant factor. 3. Cyclo heximide inhibited labelling of phosphatidylcholine from [Me-14C]choline but did not affect labelling of the aqueous choline pool. It had no effect on [2-14C]ethanolamine uptake or incorporation into phosphatidylethanolamine. 4. Hemicholinium-15 at 10mM concentrations decreased uptake and lipid labelling from the both bases. 5. There was no evidence for base competition. 6. The endogenous pool of choline was much larger than that of ethanolamine, which resulted in higher specific radioactivities for phosphatidyl-ethanolamine than for phosphatidylcholine. 7. The results can be interpreted as indicating that the kinase and phosphoryltransferase enzymes of the CDP-base pathways are separate for each phospholipid.