Some properties of phospholipid exchange proteins from rat liver.

The phospholipid exchange proteins of rat liver that catalyze the transfer of phosphatidylcholine and phosphatidylinositol from rat liver microsomes to liposomes, have been purified and characterized. Two proteins were detected with dual specificities catalyzing the transfer of both phosphatidylinositol and phosphatidylcholine. Both proteins showed a strong preference for phosphatidylinositol transferring 8 to 9 times as much of the microsomal phosphatidylinositol pool as the microsomal phosphatidylcholine pool. The two proteins had iso-electric points of 5.1 and 5.3 and were purified 300-fold and 500-fold, respectively. A protein that catalyzed specifically the transfer of phosphatidylcholine, was purified 7000-fold. This protein had an iso-electric point of 8.4 and a molecular weight of approximately 16000 calculated from Sephadex G-50 chromatography and sodium dodecylsulfate-polyacrylamide gel electrophoresis; the amino acid composition was determined. An antiserum against this protein was raised in rabbits. Treatment of a rat liver supernatant fraction with the antiserum immunoglobulin fraction demonstrated that 60% of the phosphatidylcholine transfer activity is due to this protein.