Cholinephosphotransferase in rat lung. The in vitro synthesis of dipalmitoylphosphatidylcholine from dipalmitoylglycerol.

Active substrate preparations of dipalmitoylglycerol were obtained by sonicating dipalmitoylglycerol, phosphatidylglycerol, and Tween 20 together at 65 degrees C. The apparent Vmax for cholinephosphotransferase in lung microsomes was 30 nmol/min/mg of protein for dipalmitoylglycerol-phosphatidylglycerol-Tween 20 substrate preparations and 43 nmol/min/mg of protein for dioleoylglycerol-phosphatidylglycerol-Tween 20 preparations. Sonication at 65 degrees C was required for maximal activity with dipalmitoylglycerol but not for dioleoylglycerol. Highest activity was obtained when diacylglycerol was sonicated with phosphatidylglycerol and Tween 20 although phosphatidylglycerol also increased the activity when added separately. The presence of phosphatidylglycerol was critical particularly with dipalmitoylglycerol as substrate. Phosphatidylinositol, phosphatidylserine, and phosphatidic acid were slightly active but phosphatidylcholine and phosphatidylethanolamine were inactive.