SERINE AND ETHANOLAMINE INCORPORATION INTO DIFFERENT PLASMALOGEN POOLS - SUBCELLULAR ANALYSES OF PHOSPHOGLYCERIDE SYNTHESIS IN CULTURED GLIOMA-CELLS

In cultured glioma cells, plasma membrane (PM) is enriched in phosphat idylserine (PtdSer) and plasmalogens -1'-enyl-2-acyl-sn-glycero-3-phos phoethanolamine). Serine can be a precursor of headgroups of both PtdS er and ethanolamine phosphoglycerides (PE) including plasmalogens and non-plasmalogen PE (NP-PE). Synthesis of phospholipids was investigate d at the subcellular level using established fractionation procedures and incorporation of [H-3(G)]L-serine and [1,2-C-14]ethanolamine. Spec ific radioactivity of PtdSer from [H-3]serine was 2-fold greater in PM than in microsomes, reaching maximum by 2-4 h. Labeled plasmalogen fr om [H-3]serine appeared in PM by 4 h and increased to 48 h, whereas al most no plasmalogen accumulated in microsomes within 12 h. In contrast , labeled plasmalogen from [1,2-C-14]ethanolamine appeared in both PM and microsomes at early incubation times and became enriched in PM bey ond 12 h. Thus, in glioma cells: (1) greater and faster accumulation o f labeled PtdSer in PM may reflect direct synthesis from serine within PM; (2) PM is a major source of PtdSer for decarboxylation and PE syn thesis; (3) NP-PE in both PM and microsome provides headgroup for synt hesis of plasmalogen; and, (4) plasmalogen synthesis may involve diffe rent intracellular pools depending on headgroup origin.