Tcherkez Guillaume, Farquhar Graham D
Environmental Biology Group, Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.
Funct Plant Biol. 2005 May;32(4):277-291. doi: 10.1071/FP04211.
Carbon isotope effects of enzymes involved in primary carbon metabolism are key parameters in our understanding of plant metabolism. Nevertheless, some of them are poorly known because of the lack of in vitro experimental data on purified enzymes. Some studies have focused on theoretical predictions of isotope effects. Here we show how quantum chemical calculations can be adapted for calculation of isotope effects for the Rubisco-catalysed carboxylation and oxygenation reactions and the citrate synthase reaction. The intrinsic isotope effect of the carboxylation by Rubisco appears to be much smaller than previously thought, being close to the overall isotope effect of the reaction that is, between 25 and 30 per mil. The same applies to the enzyme citrate synthase, that catalyses the first step of the Krebs cycle, with an isotope effect of around 23 per mil. Combined with the isotope effects of equilibrium reactions calculated with β-factors, the Krebs cycle then has an overall isotope effect that depletes organic acids in C.
参与初级碳代谢的酶的碳同位素效应是我们理解植物代谢的关键参数。然而，由于缺乏关于纯化酶的体外实验数据，其中一些酶鲜为人知。一些研究集中在同位素效应的理论预测上。在这里，我们展示了如何将量子化学计算应用于计算核酮糖-1,5-二磷酸羧化酶（Rubisco）催化的羧化和氧化反应以及柠檬酸合酶反应的同位素效应。Rubisco羧化反应的内在同位素效应似乎比以前认为的要小得多，接近该反应的整体同位素效应，即千分之25至30之间。催化三羧酸循环第一步的柠檬酸合酶也是如此，其同位素效应约为千分之23。结合用β因子计算的平衡反应的同位素效应，三羧酸循环的整体同位素效应会使C中的有机酸减少。
