Liver microsomes were enriched in liposomal acidic lipids by Ca2+-dependent fusion of liposomes at pH 7.0. The extent of fusion was monitored by the transfer of radioactive cholesteryl oleate. The enrichment of membranes in phosphatidylserine inhibited ethanolamine base-exchange, whereas the fusion with phosphatidylinositol inhibited both ethanolamine and serine base-exchange reactions. In contrast, these two phospholipids had scarce effects on choline base-exchange. Phosphatidic acid did not suppress any of the three base-exchange activities. Possible functional implications are discussed.
Abbreviations DTT, dithiothreitol; HEPES, 4-(2-hydroxyethyl)-1-piperazineethansulfonic acid; SHB, suerose-HEPES buffer (0.25M sucrose, 3mM HEPES, pH 7.4)