Eyzaguirre Jaime, Valdebenito David, Cardemil Emilio
Laboratorio de Bioquímica, Pontificia Universidad Católica de Chile, Santiago, Chile.
Arch Biochem Biophys. 2006 Oct 15;454(2):189-96. doi: 10.1016/j.abb.2006.08.002. Epub 2006 Aug 22.
Phosphomevalonate kinase catalyzes the phosphorylation of phosphomevalonate to diphosphomevalonate by ATP, one of the initial steps in the biosynthesis of steroids and isoprenoids. In previous studies, the enzyme from pig liver was purified and characterized, and preliminary work showed that the enzyme follows hyperbolic kinetics and a sequential mechanism. The present work is a more detailed analysis of its kinetic mechanism, using initial velocity and isotope exchange at equilibrium measurements. The results are compatible with a Bi Bi sequential ordered mechanism with phosphomevalonate as the first substrate and ADP the last product. The Km values estimated are 43+/-7 microM for Mg-ATP and 12+/-3 microM for phosphomevalonate, with a Vmax of 51+/-2 micromol min-1 mg of protein-1.
磷酸甲羟戊酸激酶催化磷酸甲羟戊酸由ATP磷酸化生成二磷酸甲羟戊酸，这是类固醇和类异戊二烯生物合成的起始步骤之一。在先前的研究中，猪肝中的该酶已被纯化和表征，初步工作表明该酶遵循双曲线动力学和有序机制。目前的工作是使用初速度和平衡时的同位素交换测量对其动力学机制进行更详细的分析。结果与以磷酸甲羟戊酸为第一底物、ADP为最后产物的双底物双产物有序机制相符。估计的米氏常数（Km值）对于Mg-ATP为43±7微摩尔，对于磷酸甲羟戊酸为12±3微摩尔，最大反应速度（Vmax）为51±2微摩尔·分钟-1·毫克蛋白质-1。
