Ml. Hernandez et al., DIVALENT METAL-IONS AS MODULATORS OF RAT-LIVER MICROSOMAL CHOLESTEROLESTERASE, Revista Espanola de Fisiologia, 49(2), 1993, pp. 107-114
The regulatory properties of the divalent metal ions Mg2+, Ca2+ and Mn
2+ on the activity and kinetic behaviour of rat liver microsomal chole
sterol esterase were studied in vitro. Me2+ 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 inhib
itory 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 che
lating agents that reversed the metal ion-induced activation. Hence, t
he maximum rate of cholesterol ester hydrolysis doubled in the presens
e of Mg2+ and activation was reversed by EDTA, whereas a significant d
ecrease in the apparent Km for cholesterol oleate was found when Ca2was added and this effect was blocked by ATP and EGTA. Both cations we
re able to reactivate cholesterol ester hydrolase activity in metal-de
pleted microsomes.