Mithieux G, Vega F V, Riou J P
Institut National de la Santé et de la Recherche Médicale, Unité 197, Faculté de Médecine Alexis Carrel, Lyon, France.
J Biol Chem. 1990 Nov 25;265(33):20364-8.
We have recently shown that the Ca.EGTA and Mg.EDTA complexes, but not free Ca2+ or Mg2+, inhibit the liver glucose-6-phosphatase (Mithieux, G., Vega, F. V., Beylot, M., and Riou, J. P. (1990) J. Biol. Chem. 265, 7257-7259). In this work, we report that, when complexed with Mg2+, two endogenous dicarboxylic keto acids (alpha-ketoglutarate (alpha-KG) and oxaloacetate (OAA] inhibit the glucose-6-phosphatase activity at low concentrations of substrate. This phenomenon is specific for complexes of Mg2+ with alpha-KG and OAA since 1) the complexes of Mg2+ with a number of other di- or tricarboxylic acids having high structural analogy with alpha-KG and OAA (oxalate, malate, succinate, citrate, aspartate, and glutamate) do not inhibit the glucose-6-phosphatase activity and 2) the Ca.alpha-KG and Ca.OAA chelates do not inhibit the glucose-6-phosphatase activity. In the presence of Mg.alpha-KG or Mg.OAA chelates, the enzyme displays sigmoid kinetics; the Hanes plots deviate from linearity, indicating the positive cooperative dependence of the velocity upon the substrate concentration. Hill coefficients (equal to 1 in the absence of the chelates) of 1.23 and 1.33 have been determined in the presence of Mg.alpha-KG and Mg.OAA complexes, respectively. The disruption of microsomal integrity by detergents abolishes the effect of Mg.alpha-KG and Mg.OAA, suggesting that the magnesium chelates inhibit the translocase component of the glucose-6-phosphatase system.
我们最近发现，乙二醇双（2-氨基乙基醚）四乙酸钙（Ca.EGTA）和乙二胺四乙酸镁（Mg.EDTA）复合物，而非游离的Ca2+或Mg2+，可抑制肝脏葡萄糖-6-磷酸酶（米蒂厄，G.，维加，F.V.，贝洛，M.，和里奥，J.P.（1990年）《生物化学杂志》265卷，7257 - 7259页）。在这项研究中，我们报告称，当与Mg2+络合时，两种内源性二羧酸酮酸（α-酮戊二酸（α-KG）和草酰乙酸（OAA））在低底物浓度下会抑制葡萄糖-6-磷酸酶活性。这种现象对于Mg2+与α-KG和OAA的复合物具有特异性，原因如下：1）Mg2+与许多其他与α-KG和OAA具有高度结构相似性的二羧酸或三羧酸（草酸盐、苹果酸盐、琥珀酸盐、柠檬酸盐、天冬氨酸盐和谷氨酸盐）形成的复合物不会抑制葡萄糖-6-磷酸酶活性；2）Ca.α-KG和Ca.OAA螯合物不会抑制葡萄糖-6-磷酸酶活性。在Mg.α-KG或Mg.OAA螯合物存在的情况下，该酶呈现S形动力学；汉尼斯图偏离线性，表明速度对底物浓度存在正协同依赖性。在Mg.α-KG和Mg.OAA复合物存在的情况下，分别测定出希尔系数为1.23和1.33（在不存在螯合物时等于1）。去污剂破坏微粒体完整性会消除Mg.α-KG和Mg.OAA的作用，这表明镁螯合物抑制了葡萄糖-6-磷酸酶系统的转位酶成分。
