Institute of Biological Chemistry, Washington State University, Pullman, Washington.
Plant Physiol. 1992 Oct;100(2):560-4. doi: 10.1104/pp.100.2.560.
In leaf tissue, carbon enters starch via the gluconeogenesis pathway where d-glycerate 3-phosphate formed from CO(2) fixation is converted into hexose monophosphates within the chloroplast stroma. In starch-containing sink organs, evidence has been obtained indicating that the flow of carbon into starch follows a different pathway whereby hexose monophosphates formed from sucrose are transported into the amyloplast, a plastid specialized in starch accumulation. In both chloroplasts and amyloplasts, the formation of ADPglucose, the substrate for starch synthase, is controlled by the activity of ADPglucose pyrophosphorylase, a key regulatory enzyme of starch synthesis localized in the plastid. Recently, an alternative pathway of starch synthesis has been proposed in which ADPglucose is synthesized from sucrose and transported directly into the plastid compartment, where it is used for starch synthesis. On the basis of the biochemical phenotypes exhibited by various plant mutants with defined genetic lesions, it is concluded that ADPglucose pyrophosphorylase is essential for starch synthesis, whereas the alternative pathway has only a minor role in this process.
在叶片组织中，碳通过糖异生途径进入淀粉，其中由 CO2 固定形成的 d-甘油酸 3-磷酸在叶绿体基质中转化为己糖单磷酸。在含有淀粉的库器官中，有证据表明，碳进入淀粉的流动遵循不同的途径，即来自蔗糖的己糖单磷酸被运输到淀粉体中，淀粉体是专门用于淀粉积累的质体。在叶绿体和淀粉体中，ADP 葡萄糖的形成，即淀粉合酶的底物，受 ADP 葡萄糖焦磷酸化酶的活性控制，该酶是位于质体中的淀粉合成的关键调节酶。最近，提出了一种淀粉合成的替代途径，其中 ADP 葡萄糖是由蔗糖合成并直接运输到质体隔室，在那里用于淀粉合成。基于具有明确遗传缺陷的各种植物突变体表现出的生化表型，可以得出结论，ADP 葡萄糖焦磷酸化酶是淀粉合成所必需的，而替代途径在该过程中仅起次要作用。
