Divalent metal ions as modulators of rat liver microsomal cholesterol esterase.
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.
Departamento de Fisiología, Facultad de Medicina y Odontología Universidad del País Vasco, Bilbao, Spain.
M L
ML
Hernández
M J
MJ
Martínez
Y
Y
Chico
I
I
Fernández de Marticorena
M
M
Lacort
B
B
Ochoa
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology*; D002712:Chlorides; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology*; D008345:Manganese / Q000494:pharmacology*; D017895:Manganese Compounds; D008862:Microsomes, Liver / Q000201:enzymology*; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley / Q000378:metabolism; D002787:Sterol Esterase / Q000378:metabolism*
D002712:Chlorides; D017895:Manganese Compounds; D015636:Magnesium Chloride; D008345:Manganese; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D004492:Edetic Acid; D002787:Sterol Esterase; D002122:Calcium Chloride; C025340:manganese chloride