Phosphatidylcholine and phosphatidylinositol exchange proteins in rat liver

The phospholipid exchange proteins in rat liver that stimulate the transfer of phosphatidylcholine and phosphatidylinositol between membranes were separated into three fractions and partially purified by acid pH precipitation, gel filtration on Sephadex G-75, and ionexchange chromatography on DEAE-cellulose and CM-cellulose. Throughout the steps of the purification, both the phosphatidylcholine exchange activity and the phosphatidylinositol exchange activity were measured by a liposome-liposome assay system, which used concanavalin A in the separation of donor and acceptor liposomes. One of the fractions was purified 172-fold and stimulated the phosphatidylcholine exchange but not the phosphatidylinositol exchange. The other two fractions were active in the stimulation of the phosphatidylinositol exchange as well as the phosphatidylcholine exchange and were purified 62-fold and 58-fold over the cell supernatant fraction with respect to the phosphatiylinsitol exchange activity. These two fractions stimulated the transfer of phosphatidylinositol from donor liposomes to acceptor liposomes initially deficient in this phospholipid.