A kinetic study of the temperature dependence of the template-directed formation of oligoguanylate (oligo(G)) on polycytidylic acid (poly(C)) from the 5′-phosphorimidazolide of guanosine (ImpG) has been carried out in the presence of Zn2+ at 40–80 °C. It is surprising that a large amount of oligo(G) was formed at 40–60 °C and a small amount of oligo(G) was detected even at 80 °C. The rate constants of the template-directed formation of oligo(G) were determined at 40–60 °C, and the same trend, the rate constants increase with the chain length, was observed as that at lower temperatures. Besides, second-order rate plots of the hydrolyses of ImpG and oligo(G) were consistent with pseudo-second-order processes in the presence of 0.04 M Zn2+. The apparent activation energy determined from the Arrhenius plots decreases in the order hydrolysis of oligo(G) > formation of 4-mer ≈ formation of 3-mer ≈ hydrolysis of ImpG > formation of 2-mer. The kinetic analysis and computer simulations demonstrate the importance of the rate of 2-mer formation to determine the efficiency of the oligo(G) formation.
研究人员在 Zn2+ 存在下,于 40-80 °C对
鸟苷的 5′-
磷酰亚胺唑内酯(ImpG)在聚
胞苷酸(poly(C))上模板定向形成寡聚
鸟苷酸盐(oligo(G))的温度依赖性进行了动力学研究。令人惊讶的是,在 40-60 ℃ 时形成了大量的寡聚(G),而在 80 ℃ 时也检测到了少量的寡聚(G)。在 40-60 ℃ 下测定了模板定向形成寡聚物(G)的速率常数,观察到与低温下相同的趋势,即速率常数随链长增加而增加。此外,在 0.04 M Zn2+ 存在下,ImpG 和寡聚(G)
水解的二阶速率图与伪二阶过程一致。从阿伦尼乌斯图中确定的表观活化能按以下顺序递减:
水解低聚物(G)>形成 4-聚合体≈形成 3-聚合体≈
水解 ImpG> 形成 2-聚合体。动力学分析和计算机模拟表明,2-聚合体的形成速率对于确定寡聚(G)形成的效率非常重要。