Le Maréchal P, Azerad R
Biochimie. 1976 Nov 13;58(9):1123-8. doi: 10.1016/s0300-9084(76)80090-9.
The conversion of 3-deoxy D-arabino heptulosonate 7-phosphate to 3-dehydroquinate by the 3-dehydroquinate synthetase from E. coli is characterized by a low but significant kinetic isotope effect for tritium carried in position-5 of DAHP, while no isotope effect was detectable for tritium in position-4. This effect was observed at different pH nad is interpreted as a result of theintermediary of a 5-ketonic form of the substrate, formed in a preliminary non limiting step during the enzymic cyclization reaction. A tentative scheme for the 3-DHQ synthetase reaction is proposed involving five steps: oxidation by NAD+ in position-5, phsophate elimination after enolization, reduction with precedently formed NADH and cyclization by attack of the 2-carbonyl by the C-7 methylene group.
大肠杆菌的3-脱氢奎尼酸合成酶将3-脱氧-D-阿拉伯庚酮糖酸7-磷酸转化为3-脱氢奎尼酸的过程中，对于DAHP 5位携带的氚具有较低但显著的动力学同位素效应，而4位的氚未检测到同位素效应。在不同pH值下均观察到这种效应，这被解释为底物的5-酮形式作为中间体在酶促环化反应的初步非限速步骤中形成的结果。提出了一个3-DHQ合成酶反应的暂定方案，包括五个步骤：5位被NAD+氧化、烯醇化后消除磷酸、被先前形成的NADH还原以及C-7亚甲基进攻2-羰基进行环化。
