Hernández M L, Martínez M J, Chico Y, Fernández de Marticorena I, Lacort M, Ochoa B
Departamento de Fisiología, Facultad de Medicina y Odontología Universidad del País Vasco, Bilbao, Spain.
Rev Esp Fisiol. 1993 Jun;49(2):107-13.
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.
体外研究了二价金属离子Mg2+、Ca2+和Mn2+对大鼠肝脏微粒体胆固醇酯酶活性和动力学行为的调节特性。Mg2+和Ca2+表现出相似的浓度和预孵育时间依赖性酯酶活性增加，在2 mM浓度时刺激作用最大。然而，Mn2+在此浓度下无作用，但在高于20 mM的浓度时表现出强烈的抑制作用。Mg2+和Ca2+对胆固醇酯酶的激活在以下方面具有选择性：i）阳离子在酶动力学常数中产生的变化，以及ii）逆转金属离子诱导激活的螯合剂。因此，在Mg2+存在下胆固醇酯水解的最大速率加倍，且激活作用可被EDTA逆转，而添加Ca2+时油酸胆固醇的表观Km显著降低，且该效应被ATP和EGTA阻断。两种阳离子都能够使金属耗尽的微粒体中的胆固醇酯水解酶活性重新激活。
