Cholesterol esterases from normal and FEC hamster liver

1. Synthetic cholesteryl esters with various acyl chain length (C2-C18) are hydrolysed by several enzymes in hamster liver. 2. The comparison of effect of inhibitors, divalent cations, detergents, pH and substrate specificity allows discrimination between four enzymes hydrolyzing cholesteryl esters, which are characterized by their enzymatic properties, two cholesterol esterases (resistant to E600) hydrolyzed medium- and long-chain cholesteryl esters, whereas short-chain cholesteryl esters were hydrolyzed by two different carboxylesterases (dramatically inhibited by E600). 3. The acid cholesterol esterase (identical to the lysosomal lipase) exhibited a pH optimum at pH 5.0 and is activated by 1 mM taurocholate. 4. The alkaline cholesterol esterase (pH optimum 7.5) is not very sensitive to the tested effectors. 5. Both acid and alkaline carboxylesterases (pH optima 5.5 and 7.5), were characterized by their strict dependence on divalent cations (Mn2+ or Mg2+). 6. The acid carboxylesterase was inhibited by increasing concentrations of Triton X-100, whereas the alkaline carboxylesterase was dramatically activated by 2 g/l Triton X-100. 7. No significant difference was observed in activities of cholesterol esterases or carboxylesterases between normal and FEC hamster livers.