PATHWAYS OF MEMBRANE PHOSPHOLIPID-SYNTHESIS IN THE MYXOMYCETE PHYSARUM-POLYCEPHALUM

In the present study we investigated the synthesis of membrane phospho lipids in the myxomycete Physarum polycephalum during the logarithmic growth phase using [P-32]orthophosphoric acid and [C-14]ethanolamine. The label incorporation into phospholipids was shown to increase in th e following order: phosphatidylcholine (PC) < phosphatidylserine (PS) < phosphatidylethanolamine (PE) < phosphatidylinositol (PI) < phosphat idic acid. For PE and PI, the rates of synthesis were 2-fold higher th at those required for cell duplication, It has been established that P S is not synthesized from PE or PC and is not the main precursor of PE or PC. Only a minor part of PC is synthesized through methylation of PE; its major part is synthesized by coupling of two precursors to dia cylglycerol; one of these precursors is phosphorylated inside the cell , the other is absorbed from the environment in phosphorylated form.