Separation and differential activation of rat liver cytosolic cholesteryl ester hydrolase, triglyceride lipase and retinyl palmitate hydrolase by cholestyramine and protein kinases.

Cholesteryl ester hydrolase (CEH), triacylglycerol lipase (TGL) and retinyl palmitate hydrolase (RPH) were measured in 104,000 x g supernatants from rat liver under optimal conditions for measurement of cytosolic CEH. Similar levels of hydrolytic activity were seen with oil droplet dispersions of cholesteryl oleate, trioleoylglycerol and retinyl palmitate. No cytosolic TGL activity was seen with substrate presented in the triton-albumin emulsion used for measurement of lipoprotein lipase-like TGL associated with hepatic plasma membrane. Cytosolic CEH, TGL and RPH were differentially partially purified by both ammonium sulfate precipitation and anion exchange fast protein liquid chromatography (FPLC). Of the tree activities, only CEH was stimulated by cholestyramine feeding and by activators of protein kinases A and C. All three activities were inhibited by alkaline phosphatase treatment, although to different degrees. It is concluded that these activities are catalyzed by at least three differentially regulated enzymes with a high degree of specificity for their respective substrates.