Regulation of phosphatidylcholine biosynthesis in mammalian cells. III. Effects of alterations in the phospholipid compositions of Chinese hamster ovary and LM cells on the activity and distribution of CTP:phosphocholine cytidylyltransferase.

The activity and subcellular distribution of CTP:phosphocholine cytidylyltransferase in LM and Chinese hamster ovary cells in which the phospholipid composition had been altered by supplementary feeding with choline analogues were examined. Decreased levels of cellular phosphatidylcholine with corresponding increased levels of either phosphatidylethanolamine, phosphatidylmonomethylethanolamine, or phosphatidyldimethylethanolamine resulted in increased CTP:phosphocholine cytidylyltransferase activity in cell homogenates. In addition, a significantly larger fraction of the total cytidylyltransferase activity was membrane-bound in these cells. The activity of the cytidylyltransferase from cytosolic extracts of both cell types was found to be greatly increased when assayed in the presence of either phosphatidylmonomethyl ethanolamine or phosphatidyldimethylethanolamine. The lysophosphatide forms of these lipids were found to be poor activators of the cytidylyltransferase. These findings suggest that the regulation of phosphatidylcholine biosynthesis is at least partially dependent on information transfer from membranes to CTP: phosphocholine cytidylyltransferase. That is, in the presence of phosphatidylcholine-deficient membranes of cytidylyltransferase becomes activated and associated with the membranes.