Satoh Y
Biochim Biophys Acta. 1986 Aug 15;872(3):177-82. doi: 10.1016/0167-4838(86)90269-4.
The mitochondrial phosphoenolpyruvate carboxykinase (GTP:oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32), purified from chick embryo liver, was synergistically activated by a combination of Mn2+ and Mg2+ in the oxaloacetate ---- H14CO-3 exchange reaction. Increases in the Mg2+ concentration caused decreases in the K0.5 value of Mn2+ in line with the earlier finding that the enzyme was markedly activated by low Mn2+ (microM) plus high Mg2+ (mM). In the presence of 2.5 mM Mg2+, increases in the Mn2+ level first enhanced the activity of phosphoenolpyruvate carboxykinase, and then suppressed it to the maximal velocity shown in the presence of Mn2+ alone. Kinetic studies showed that high Mn2+ inhibited the activity of Mg2+ noncompetitively, and those of GTP and oxaloacetate uncompetitively. The inhibition constant for oxaloacetate (K'i = 550 microM) was lower than that of Mg2+ (Ki = K'i = 860 microM) or GTP (K'i = 1.6 mM), and was nearly equal to the apparent half-maximal inhibition concentration of Mn2+. These results suggested that Mn2+ can play two roles, of activating and suppressing phosphoenolpyruvate carboxykinase activity in the presence of high Mg2+.
从鸡胚肝脏中纯化得到的线粒体磷酸烯醇式丙酮酸羧激酶（GTP：草酰乙酸羧基裂解酶（转磷酸化），EC 4.1.1.32），在草酰乙酸----H14CO-3交换反应中，被Mn2+和Mg2+的组合协同激活。Mg2+浓度的增加导致Mn2+的K0.5值降低，这与早期发现该酶被低Mn2+（微摩尔）加高Mg2+（毫摩尔）显著激活的结果一致。在2.5 mM Mg2+存在的情况下，Mn2+水平的增加首先增强了磷酸烯醇式丙酮酸羧激酶的活性，然后将其抑制到仅存在Mn2+时所示的最大速度。动力学研究表明，高Mn2+非竞争性抑制Mg2+的活性，对GTP和草酰乙酸则为非竞争性抑制。草酰乙酸的抑制常数（K'i = 550 microM）低于Mg2+（Ki = K'i = 860 microM）或GTP（K'i = 1.6 mM），且几乎等于Mn2+的表观半最大抑制浓度。这些结果表明，在高Mg2+存在的情况下，Mn2+可以发挥激活和抑制磷酸烯醇式丙酮酸羧激酶活性这两种作用。
