Effects of phosphatidylcholine/phosphatidylethanolamine composition in cholesteryl ester-micellar substrates on neutral cholesterol esterase activity

The effect of phospholipid composition in cholesteryl ester (CE)-micellar s ubstrates on neutral cholesterol esterase (N-CEase) activity was examined. N-CEase preparation was incubated with micelles composed of cholesteryl-[1- C-14]-oleate, sodium taurocholate, and phosphatidylcholine (PC)/phosphatidy lethanolamine: (PE) at varying ratios (%PE:0 = PC only, 17, 33, 50, 66, 83) . The activity increased dependently with the increase in PE content; the a ctivity with the micelles containing the highest ratio of PE was 2.5-fold c ompared with the micelles consisting of PC only. V-max with the micelles of 83, 66, and 50% PE was 3.1-, 2.7-,and 1.9-fold, respectively, compared wit h the micelles of PC only. Each micellar Preparation was chromatographed th rough a Superose 6 column by the FPLC system. in 66 and 83% PE-containing m icelles, PC, PE, CE, and part of sodium taurocholate eluted completely toge ther in a single peak, whereas in micelles with 33 and 50% PE they eluted l oosely together. The micelles with PC only or 17% PE formed PC-micelles wit hout including CE and PE. It is concluded that PE plays a critical role in the formation of CE micelles with PC, and in the interaction with N-CEase. The CE-micelles with 66-83% PE serve as substrates for sensitive and-reprod ucible N-CEase assay. (C) 1999 Academic Press.