Job C, Soulié J M, Job D
Centre de Biochimie et de Biologie Moléculaire du Centre National de la Recherche Scientifique, Marseille, France.
Biochem J. 1988 May 15;252(1):55-63. doi: 10.1042/bj2520055.
A kinetic study of productive RNA chain elongation indicates that adenosine 5'-[beta gamma-imido]triphosphate can serve as substrate in reactions catalysed by purified wheat-germ RNA polymerase II on a poly[d(A-T)] template. However, in contrast with the results obtained with the natural substrate ATP, the double-reciprocal plots, 1/velocity versus 1/[nucleotide], are not linear but characteristic of apparent negative co-operativity. The extent of the kinetic co-operativity is modified when the reactions are conducted in the additional presence of fixed amounts of an alternative substrate such as ATP or inhibitors such as dATP or cordycepin triphosphate. Analogous results are obtained whether the reactions are carried out in the presence of Mg2+ or Mn2+ as the metal ion cofactor. However, the data show that with Mn2+ the RNA polymerase is less specific in substrate recognition than with Mg2+. Tentative kinetic models are proposed to account for the rate measurements.
对有活性的RNA链延伸进行的动力学研究表明,腺苷5'-[βγ-亚氨基]三磷酸可作为纯化的小麦胚芽RNA聚合酶II在聚[d(A-T)]模板上催化的反应中的底物。然而,与天然底物ATP得到的结果相反,双倒数图(1/速度对1/[核苷酸])不是线性的,而是表现出明显的负协同性特征。当反应在固定量的替代底物(如ATP)或抑制剂(如dATP或三磷酸虫草素)存在的情况下进行时,动力学协同性的程度会发生改变。无论反应是在Mg2+还是Mn2+作为金属离子辅因子存在的情况下进行,都能得到类似的结果。然而,数据表明,与Mg2+相比,Mn2+存在时RNA聚合酶在底物识别方面的特异性较低。提出了初步的动力学模型来解释速率测量结果。