Choline biosynthesis by a preparation enriched in synaptosomes from rat brain.

It is widely held that brain cells are unable to synthesize choline de novo, and that the only source of this compound for brain acetylcholine or membrane biosynthesis is the choline or choline-containing phospholipids taken up from the circulation. This notion has been difficult to reconcile with observations that there is a net efflux of choline from the brain. Recently we and others have demonstrated that various preparations of mammalian brain contain enzymes, the phosphatidylethanolamine N-methyltransferase (PeMT), which catalyse the synthesis of phosphatidylcholine (PC), using S-adenosylmethionine (SAM) as a methyl donor for the stepwise methylation of phosphatidylethanolamine (PE). The highest specific activity of PeMT was present in synaptosomal preparation. We now report that rat brain synaptosomal preparations can also metabolize the PC generated by PeMT to liberate free choline.