Kapuler A M, Spiegelman S
Proc Natl Acad Sci U S A. 1970 Jun;66(2):539-46. doi: 10.1073/pnas.66.2.539.
Base selection by the Qbeta-replicase and E. coli transcriptase has been studied using substrate analogs. Six analogs with normal hydrogen-bonding sites were polymerized by both enzymes. Three analogs containing ring substitutions which affect the conformation at the glycosyl bond would not substitute for their normal congeners. The remaining analog was an excellent substrate for the transcriptase but not the replicase.The results imply that the base selection procedure has stringent requirements for substrate conformation. Part of the restriction may derive from the requirement that template and substrates conform to the stereochemical constraints of a double helix. In the Qbeta-replicase reaction, synthesis in the presence of substrate analogs displayed abortive kinetics, implying that the replicase reaction can be uniquely curtailed by substrate analogs.
已使用底物类似物研究了Qβ复制酶和大肠杆菌转录酶的碱基选择。六种具有正常氢键位点的类似物可被这两种酶聚合。三种含有影响糖基键构象的环取代的类似物不能替代其正常同类物。其余的类似物是转录酶的优良底物，但不是复制酶的优良底物。结果表明，碱基选择过程对底物构象有严格要求。部分限制可能源于模板和底物符合双螺旋立体化学限制的要求。在Qβ复制酶反应中，在底物类似物存在下的合成显示出无效动力学，这意味着复制酶反应可被底物类似物独特地抑制。
