Studies on cholesterol esterase in cultured rabbit smooth muscle cells

Acid and neutral cholesterol esterases (CEases) in cultured rabbit smooth muscle cells (SMC) were examined. The optimal pH of acid CEase was 4.5 and its apparent Km was 83 microM. The optimal pH of neutral CEase was 7.5 and its apparent Km was 38 microM. CEases were most active with substrate vesicles prepared with phosphatidylcholine. Acid CEase hydrolyzed cholesteryl [1-14C]oleate labeled LDL (LDL-CE), but neutral CEase did not. Incubation with LDL increased the acid and neutral CEase activities of SMC, but incubation with acetylated-LDL did not increase their activities.