Modulation of phosphatidylcholine biosynthesis in celery by exogenous fatty acids

The effects of C-16 and C-18 fatty acids on the synthesis of phosphatidylch oline were studied in Apium graveolens cell suspension cultures and postmit ochondrial supernatants. When cells were exposed to exogenous oleic acid, t he rate of phosphatidylcholine biosynthesis increased 1,4-fold within 5 min of the addition of the fatty acid to the culture medium. The sensitivity o f microsomal CTP:cholinephosphate cytidylyltransferase (EC 2.7.7.15) to sat urated and unsaturated fatty acids was monitored through the addition of un esterified fatty acids to postmitochondrial supernatants. The saturated fat ty acids, palmitic and stearic, appeared to have little effect on CTP:choli nephosphate cytidylyltransferase activity, whereas exposure to oleic, linol eic and cis-vaccenic acids resulted in significant increases in enzyme acti vity. Optimal microsomal CTP:cholinephosphate cytidylyltransferase activiti es were achieved by the incubation of postmitochondrial supernatants with 5 00 mu M oleate. The exogenous fatty acids were found to be incorporated int o microsomal membranes in their unesterified form. Removal of unesterified fatty acids by incubation of microsomal membranes with defatted bovine seru m albumin resulted in the reduction of microsomal CTP:cholinephosphate cyti dylyltransferase activity; demonstrating that the enzyme requires unesterif ied unsaturated fatty acids. (C) 1998 Elsevier Science Ltd. All rights rese rved.