Isolation of a protein from beef liver which specifically stimulates the exchange of phosphatidylcholine

Abstract

1. 1. The soluble protein fraction from beef liver contains a protein which stimulates phospholipid exchange. The activity of this protein has been assayed by determining the stimulation of phosphatidylcholine exchange either between 32P-labeled mitochondria and microsomes or between mitochondria labeled with [14C]phosphatidylcholine and microsomes.

2. 2. The phospholipid exchange protein from beef liver has been purified 310-fold with an overall recovery of activity of 15 %. (NH4)2SO4 precipitation, ion-exchange chromatography on DEAE-Sephadex A-50 and gel filtration on Sephadex G-75 and Sephadex G-50 were used.

3. 3. The isolated phospholipid exchange protein stimulated specifically the exchange of phosphatidylcholine between mitochondria and microsomes. This specificity was also apparent in the phospholipid exchange between microsomes and liposomes consisting of egg yolk phosphatidylcholine and between mitochondria and liposomes consisting of egg yolk phosphatidylcholine (70 mole %) and rat liver phosphatidylethanolamine (30 mole %).