Tcherkez Guillaume, Farquhar Graham, Badeck Franz, Ghashghaie Jaleh
Laboratoire d'écophysiologie végétale, UMR 8079, Bât. 362, Centre scientifique d'Orsay, Université Paris XI, 91405 Orsay Cedex, France.
Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, GPO Box 475 Canberra, ACT 2601, Australia.
Funct Plant Biol. 2004 Oct;31(9):857-877. doi: 10.1071/FP04053.
The origin of the non-statistical intramolecular distribution of C in glucose of C plants is examined, including the role of the aldolisation of triose phosphates as proposed by Gleixner and Schmidt (1997). A modelling approach is taken in order to investigate the relationships between the intramolecular distribution of C in hexoses and the reactions of primary carbon metabolism. The model takes into account C-C bond-breaking reactions of the Calvin cycle and leads to a mathematical expression for the isotope ratios in hexoses in the steady state. In order to best fit the experimentally-observed intramolecular distribution, the values given by the model indicate that (i), the transketolase reaction fractionates against C by 4-7‰ and (ii), depending on the photorespiration rate used for estimations, the aldolase reaction discriminates in favour of C by 6‰ during fructose-1,6-bisphosphate production; an isotope discrimination by 2‰ against C is obtained when the photorespiration rate is high. Additionally, the estimated fractionations are sensitive to the flux of starch synthesis. Fructose produced from starch breakdown is suggested to be isotopically heavier than sucrose produced in the light, and so the balance between these two sources affects the average intramolecular distribution of glucose derived from stored carbohydrates. The model is also used to estimate photorespiratory and day respiratory fractionations that appear to both depend only weakly on the rate of ribulose-1,5-bisphosphate oxygenation.
研究了C₃植物葡萄糖中碳的非统计分子内分布的起源，包括Gleixner和Schmidt（1997年）提出的磷酸丙糖醛醇化作用的作用。采用建模方法来研究己糖中碳的分子内分布与初级碳代谢反应之间的关系。该模型考虑了卡尔文循环中的碳-碳键断裂反应，并得出了稳态下己糖同位素比率的数学表达式。为了最佳拟合实验观察到的分子内分布，模型给出的值表明：（i）转酮醇酶反应使碳分馏4-7‰；（ii）根据用于估算的光呼吸速率，在果糖-1,6-二磷酸生成过程中醛缩酶反应使碳优先富集6‰；当光呼吸速率较高时，对碳的同位素分馏为2‰。此外，估计的分馏对淀粉合成通量敏感。淀粉分解产生的果糖在同位素上比光下产生的蔗糖重，因此这两种来源之间的平衡影响了储存碳水化合物衍生的葡萄糖的平均分子内分布。该模型还用于估计光呼吸和日间呼吸分馏，它们似乎都仅微弱地依赖于1,5-二磷酸核酮糖的氧化速率。
