Biogenesis of endoplasmic reticulum phosphatidylcholine: Translocation of intermediates across the membrane bilayer during methylation of phosphatidylethanolamine

摘要: Phosphatidylethanolamine of rat liver microsomes is rapidly methylated by S-adenosyl[methyl-14C]methionine to produce phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine and phosphatidylcholine. Using phospholipase C as a probe, on both opened (0.4% taurocholate or French pressure cell treatment) unopened microsomes, it demonstrated that phosphatidylcholine labelled in the inner leaflet bilayer and, greater extent, outer leaflet. Phosphatidyl-N,N-dimethylethanolamine pool sequestered from open closed vesicles. Phosphatidyl-N-monomethylethanolamine similarly pool. When containing phosphatidyl-N-monomethylethanolamine were incubated with unlabeled S-adenosylmethionine, these phospholipids This metabolism was inhibited S-adenosylhomocysteine. Trypsin treatment 95% incorporation 14CH3 into no effect Therefore, are apparently synthesized enzymes located at surface microsomal membranes. These observations suggest initial methylation phosphatidylethanolamine takes place transferred However, also which does not equilibrate Phosphatidylcholine leaflets uniformly injection [14C]methionine, vivo.