Phosphatidylcholine and phosphatidylinositol exchange proteins in pig liver.

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Abstract
The pH 5.1 supernatant fraction of pig liver homogenate stimulated the transfer of [32P]phosphatidylcholine and [32P]phosphatidylinositol from donor liposomes to acceptor liposomes. Purification of the proteins which catalyzed the exchanges, yielded 5 partially purified preparations. A phospholipid exchange protein was purified 63-fold in one of the preparations and the protein was specific for phosphatidylcholine exchange. The MW and isoelectric point of the protein were 19,000 and 5.6, respectively. The other 4 preparations contained partially purified phospholipid exchange proteins which catalyzed the exchanges of phosphatidylinositol as well as phosphatidylcholine. The MW and the isoelectric points of the phosphatidylcholine-phosphatidylinositol exchange proteins were 19,000 and 4.7 and 19,000 and 4.8 for the proteins in the 2nd preparation and 21,000 and 4.5 for the protein in the 3rd preparation. These parameters in the other 2 preparations were tentatively estimated as 24,000 and 5.6 and 18,000 and 4.6. Neither sulfhydryl-binding reagents nor trypsin digestion inactivated the activity of the phosphatidylcholine specific exchange protein. Sulfhydryl-binding reagents and trypsin digestion inactivated all the phosphatidylinositol exchange activities of the partially purified exchange proteins and the phosphatidylcholine exchange activities which were presumably associated with the phosphatidylinositol exchange proteins.