Stimulation of phospholipase A2 activity by high osmotic pressure on cholesterol-containing phospholipid vesicles

The hydrolytic action of porcine pancreatic phospholipase A2 (PLA2) on cholesterol-containing dipalmitoylphosphatidylcholine liposomes was studied under various osmotic conditions by means of the phase transition release (PTR) technique. A reduced rate in the release of carboxyfluorescence (CF) from the cholesterol-containing liposomes was observed with treatment by PLA2 concomitant with the decrease in its enzymatic activity. However, the reduced PLA2 activity was elevated about 5-fold in medium of high osmotic pressure. This evidence suggests that high osmotic pressure might be responsible for the molecular packing at the bilayer surface or the high curvature of liposomal membrane structure.