Effect of phospholipids on lipase activity in rat arterial wall homogenate

Triolein hydrolyzing activity in homogenates of the rat arterial wall was studied. Two optimal pH values were observed around 5.0 (acid lipase) and 7.0 (neutral lipase). Neutral lipase activity was enhanced by serum and was inhibited by 1 M NaCl but was not inhibited by protamine. Heparin decreased the acid lipase activity. A 1-mM solution of Cu2+ ion and Zn+2 ion decreased both lipase activities. The activities of both acid and neutral lipases were increased by the addition of rat serum (2 micrograms protein serum/ml) and were decreased by the addition of more than 5 micrograms protein serum/ml. The activities of neutral and acid lipases were increased by the addition of 0.25 mM phosphatidylcholine and phosphatidylserine. Both lipase activities were decreased by the addition of 0.25 mM phosphatidylethanolamine. The addition of 0.25 mM sphingomyelin increased neutral lipase activity and decreased acid lipase activity. At concentrations higher than 2 mM, these phospholipids decreased the activities of both lipases. These results suggest that at least acid and neutral lipases exist in the arterial wall cells, and their activities might be modified by phospholipids.