Catalytic properties of the purified rat hepatic cytosolic cholesteryl ester hydrolase.

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 C4-C18 fatty acids, in sharp contrast to microsomal esterases which hydrolyze PNP-acetate more efficiently. Zn2+, Cu2+, Cd2+, Hg2+, 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.