A POSSIBLE RATE-LIMITING FUNCTION OF CHLOROPLAST HEXOSEMONOPHOSPHATE ISOMERASE IN STARCH SYNTHESIS OF LEAVES
A POSSIBLE RATE-LIMITING FUNCTION OF CHLOROPLAST HEXOSEMONOPHOSPHATE ISOMERASE IN STARCH SYNTHESIS OF LEAVES
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DOI：
10.1016/0304-4165(85)90004-2
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发表时间：
1985-01-01
期刊：
影响因子：
--
通讯作者：
DIETZ, KJ
中科院分区：
文献类型：
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作者：
DIETZ, KJ
测量从各种植物的叶子中非水分离的叶绿体中的果糖 6-磷酸和葡萄糖 6-磷酸水平。光照下葡萄糖 6-磷酸与果糖 6-磷酸之比的大幅下降表明，在高速进行光合作用的菠菜和红甜菜叶子中，磷酸己糖异构酶反应已偏离平衡状态。葡萄糖 6-磷酸与果糖 6-磷酸之比的降低与叶绿体 3-磷酸甘油酸水平的增加相关，3-磷酸甘油酸被证明是叶绿体磷酸六糖异构酶的竞争性抑制剂。其他代谢物，尤其是反应产物、葡萄糖6-磷酸和自然条件下基质中存在的浓度的离子，导致己糖单磷酸异构酶的正向反应速率进一步降低。当空气中O2浓度从21%降低到2%时，叶片光合作用速率和6-磷酸葡萄糖与6-磷酸果糖的比值均增加； 3-磷酸甘油酸浓度和淀粉合成下降。结果通过ADP葡萄糖焦磷酸化酶的激活和3-磷酸甘油酸对磷酸己糖异构酶的抑制来解释。当 ADP 葡萄糖焦磷酸化酶被激活时，磷酸己糖异构酶似乎在淀粉合成中发挥限速功能。
Levels of fructose 6-phosphate and glucose 6-phosphate were measured in chloroplasts which had been isolated non-aqueously from leaves of various plants. A large decrease in the ratio of glucose 6-phosphate to fructose 6-phosphate in the light indicated considerable displacement of the hexosephosphate isomerase reaction from equilibrium in leaves of spinach and red beet which were photosynthesizing at high rates. The decrease in the ratio of glucose 6-phosphate to fructose 6-phosphate was correlated with an increase in the chloroplastic level of 3-phosphoglyceric acid, which proved to be a competitive inhibitor of chloroplast hexosephosphate isomerase. Other metabolites, especially the product of the reaction, glucose 6-phosphate, and ions in concentrations as present in the stroma under natural conditions, cause a further reduction in the rate of the forward reaction of the hexosemonophosphate isomerase. When the concentration of O2 in air was decreased from 21 to 2%, both the rate of leaf photosynthesis and the ratio of glucose 6-phosphate to fructose 6-phosphate increased; the concentration of 3-phosphogylceric acid and starch synthesis decreased. The results are explained in terms of activation of ADPglucose pyrophosphorylase and of inhibition of hexosephosphate isomerase by 3-phosphogylceric acid. Hexosephosphate isomerase appears to assume a rate-limiting function in starch synthesis in the light when ADP glucose pyrophosphorylase is activated.