1979 Volume 6 Issue 4 Pages 549-552
The mechanism of regulation of cholesterol esterase (E. C. 3. 1. 1. 13) in rat arterial wall was investigated. Cholesterol oleate [1-14C], sonicated with phosphatidylcholine, was used as a substrate. The enzyme has pH optima around 4.5 and 7.5. The acid and neutral cholesterol esterases were found to be mainly located in lysosomal and microsomal fraction, respectively, by differential ultracentrifugation method. Both enzyme activities were remarkably increased when the substrate which was prepared with phosphatidylcholine or phosphatidylserine was used. On the other hand, no increase in enzyme activity was observed with phosphatidylethanolamine or sphingomyelin.
Acid cholesterol esterase activity was increased when lower concentration of VLDL, (1.5μg/tube of protein concentration) was added to the reaction mixture, but it was decreased when a 12μg/tube of protein of VLDL or LDL or HDL was added. Neutral cholesterol esterase activity was increased by addition of each lipoprotein. When apoVLDL or apoLDL or apoHDL was added, both cholesterol esterase activities were decreased.
Further experiments are now in progress on the mechanism of regulation of cholesterol esterases.
