Phospholipid metabolism inPlasmodium-infected erythrocytes: guidelines for further studies using radioactive precursor incorporation

Abstract

SUMMARYThe biosynthesis of phospholipids is extensive inPlasmodium knowlesi-infected simian erythrocytes due to the synthesis of membranes by this single-cell eukaryote in a host erythrocyte devoid of any pathway for lipid biosynthesis. In the present paper, we show that the incorporation of [3H]glycerol, which reflectsde novobiosynthesis, is better studied at 300 μM−1 mM than at the trace doses, since this non-physiological precursor does not modify the amount of phosphatidylcholine biosynthesis from [3H]choline. Time-course incorporation of radioactive glycerol, oleate, lysophosphatidylcholine, choline, and inositol in RPMI 1640 medium containing nutrients for lipid synthesis showed that the optimum incubation time for phospholipid studies is 60–90 min, after which radioactive incorporation slows considerably. On the other hand, studies with [14C]serine revealed that incubation for 2–3 h is necessary for isotopic labelling of phosphatidylcholine via phosphatidylserine decarboxylation and phosphatidylethanolamineN-methylation. Incorporation of the various fatty acids into individual lipids was related to the molecular species composing each of them. Studies with [14C palmitoyl] lysophosphatidylcholine showed a very fast intracellular release of radioactive fatty acids, which indicates a potent lysophospholipase activity. Taken together, these data define the indispensable conditions for an experimental system suitable for further studies.