水分子辅助的一碳单元转移机理的密度泛函研究

为验证甘氨酰胺转甲酰基酶 (Glycinamideribonucleotidetransformylase ,GARTfase)催化的一碳单元转移反应是嘌呤“从头合成”过程中一个关键步骤的实验推测 ,用B3LYP方法 ,在 6 31G 基组水平上研究了GARTfase催化反应中水分子辅助的一碳单元转移机理 .该反应一共有两条可能的反应通道 :协同的 (patha)和分步的(pathb) ,计算表明 ,后者具有较低势垒 ,更占优势 .计算结果较好地证实了实验假设 ,并进一步表明 :水分子的参与能够缓解体系的张力 ,更有利于一碳单元转移反应的进行 .

A Density Functional Theory Study of the Water-assisted Mechanism in One-carbon unit Transfer

The one-carbon unit transfer reaction catalysed by glycinamide ribonucleotide transformylase (GAR Tfase) is a key step in the de novo purine biosynthetic pathway. In order to give a theoretical research of the assumption from the experiments, the water-assisted mechanism in GAR Tfase catalysed one-carbon unit transfer reaction has been investigated by a Density Functional Theory method, B3LYP, at 6-31G* basis level. There are two possible reaction channels for the whole reaction, one is concerted (path a) and the other is stepwise (path b). The water molecule serve as a bridge to connect the proton donor to the proton acceptor. All the transition states in both paths have a six-membered ring in their structures due to the joint of the water molecule. The calculations show that the latter is preferable to the former due to the lower energy barriers. The results have verified the presumption from experiments, and proved that the joint of a water molecule can relax the strong strain in the unstable system, so it is propitious to the whole reaction.