Catalytic Properties of the Purified Rat Hepatic Cytosolic Cholesteryl Ester Hydrolase

Abstract The purified enzyme hydrolyzed cholesteryl oleate, cholesteryl linoleate, and triolein at similar rates over a broad range of concentrations. Hydrolytic activity was relatively low with p -nitrophenyl acetate, but much higher with PNP-esters of the more lipophilic C 4 -C 18 fatty acids, in sharp contrast to microsomal esterases which hydrolyze PNP-acetate more efficiently. Zn 2+ , Cu 2+ , Cd 2+ , Hg 2+ , and phenylmethylsulfonyl fluoride inhibited, whereas N-ethyl maleimide and iodoacetamide stimulated activity of the pure enzyme. Limited trypsin digestion selectively inhibited cholesteryl esterase activity with retention of activity toward PNP-octanoate, suggesting involvement of a trypsin-labile loop in the lipophilic substrate binding pocket.