Phosphatidylcholine transfer activity in human erythrocyte hemolysate.

Phosphatidylcholine (PC) transfer activity was found in human erythrocyte hemolysate. The transfer activity was assayed by the ESR peak height increase when spin-labeled PC vesicles were incubated with egg yolk PC vesicles. The transfer activity was isolated from hemoglobin by an ion exchange chromatography followed by gel filtration. The partial purification resulted in a 405-fold increase in the specific transfer activity compared with that of the hemolysate. The molecular weight of the PC transfer protein was estimated to be 23,000 by gel filtration. The transfer activity was inactivated by heat-treatment at 75 degrees C for 10 min. Phosphatidylserine vesicles strongly inhibited the activity. Half-maximal inhibition occurred on addition of 0.24 mol% of phosphatidylserine vesicles to the incubation mixture. Ca2+ restored the activity. The transfer protein was quite similar to the PC transfer protein obtained from bovine liver cytosol.