Abstract
The hydrolysis of IDL-cholesterol oleate by carboxyl esterase was examined and its role was evaluated. Purified human serum carboxyl esterase catalyzed the hydrolysis of cholesterol oleate more for β-VLDL and IDL than for LDL and HDL. Incubation of β-VLDL[3H]cholesterol linoleate with LCAT deficient patients' serum or normal human serum in the presence of LCAT inhibitor (Sand-508) formed free[3H]cholesterol. When the reaction mixture was applied to gel filtration, the ratio of [3H]cholesterol to total [3H]cholesterol ester in HDL was the highest among the various lipoprotein fractions.
These results suggest that free cholesterol generated by carboxyl esterase from IDL is transfered to HDL so as to promote the catabolism of IDL. This hypothesis is also consistant with the clinical observation that hyperlipidemia II, which had high serum cholesterol esterase activity, showed a low incidence of IDL (midband) compared to that which showed low serum cholesterol esterase activity.
