Synthesis of lecithin (phosphatidylcholine) from phosphatidylethanolamine in bovine brain

Choline molecules are needed for the synthesis of acetylcholine and phospholipids in the mammalian brain. An enzymatic activity capable of forming lecithin (phosphatidylcholine) from the step-by-step methylation of phosphatidylethanolamine is identified in the bovine brain. This enzyme(s), phosphatidylethanolamine-N-methyltransferase (EC 2.1.1.17), is localized in the synaptosomal fraction of bovine caudate nucleus, uses S-adenosylmethionine as the methyl donor (apparent K_m = 20 μM), and has a V_max of 50–60 pmol/mg protein × h (i.e. about 1% of that found in rat liver). The brain may be able to meet some of its choline requirements by de novo synthesis.