Divalent metal ions as modulators of rat liver microsomal cholesterol esterase

M.L. Hernández
M.J. Martínez
Y. Chico
I. de Marticorena
M. Lacort
B. Ochoa
63

Abstract

The regulatory properties of the divalent metal ions Mg2+, Ca2+ and Mn2+ on the activity and kinetic behaviour of rat liver microsomal cholesterol esterase were studied in vitro. Mg2+ and Ca2+ exhibited similar concentration and preincubation time-dependent increases in esterase activity, with maximal stimulation at a concentration of 2 mM. However, Mn2+ had no effect at this concentration but displayed a potent inhibitory effect at concentrations above 20 mM. Activation of cholesterol esterase by Mg2+ and Ca2+ was selective in relation to i) the changes that cations produced in the enzyme kinetic constants, and ii) the chelating agents that reversed the metal ion-induced activation. Hence, the maximum rate of cholesterol ester hydrolysis doubled in the presence of Mg2+ and activation was reversed by EDTA, whereas a significant decrease in the apparent Km for cholesterol oleate was found when Ca2+ was added and this effect was blocked by ATP and EGTA. Both cations were able to reactivate cholesterol ester hydrolase activity in metal-depleted microsomes.

Keywords:
Chlorides, Manganese Compounds, Adenosine Triphosphate/pharmacology, Animals, Calcium Chloride/pharmacology, Edetic Acid/pharmacology, Egtazic Acid/pharmacology, Enzyme Activation/drug effects, Female, Kinetics, Liver/enzymology, Magnesium Chloride/pharmacology, Manganese/pharmacology, Microsomes, Phosphorylation, Rats, Sprague-Dawley/metabolism, Sterol Esterase/metabolism, Cholesterol esterase, Divalent cations, Liver microsomes

Authors

M.L. Hernández
M.J. Martínez
Y. Chico
I. de Marticorena
M. Lacort
B. Ochoa


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