A cytosolic ADP-glucose pyrophosphorylase is a feature of graminaceous endosperms, but not of other starch-storing organs
A cytosolic ADP-glucose pyrophosphorylase is a feature of graminaceous endosperms, but not of other starch-storing organs
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DOI：
10.1104/pp.125.2.818
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发表时间：
2001-02-01
期刊：
影响因子：
7.4
通讯作者：
ap Rees, T
中科院分区：
文献类型：
--
作者：
Beckles, DM;Smith, AM;ap Rees, T
通过两种方式研究了淀粉储存器官中adp -葡萄糖（Glc）焦磷酸化酶（AGPase）的质体外异构体的发生。首先，通过比较未栽培的Hordeum品种与栽培大麦（Hordeum vulgare）胚乳中酶活性和蛋白质的细胞内分布，研究了在谷物驯化过程中产生质体外异构体的可能性。与栽培大麦一样，普通大麦的AGPase。自发乳和鼠乳由一个主要的外质体和一个次要的质体异构体组成。其次，ADP-Glc与UDP-Glc的比值被用作AGPase活性在广泛的淀粉合成器官中的细胞内位置的指示。在主要在细胞质中合成UDP-Glc和ADP-Glc的器官中，由于AGPase和UDP-Glc焦磷酸化酶催化的反应将偶联并接近平衡，因此该比率预计会很高。本研究表明，禾草胚乳中ADP-Glc含量和ADP-Glc / UDP-Glc比值高于其他淀粉储存器官。综上所述，胞外AGPase在禾草胚乳中ADP-Glc合成中起重要作用，而在其他淀粉储存器官中不起作用。
The occurrence of an extra-plastidial isoform of ADP-glucose (Glc) pyrophosphorylase (AGPase) among starch-storing organs was investigated in two ways. First, the possibility that an extra-plastidial isoform arose during the domestication of cereals was studied by comparing the intracellular distribution of enzyme activity and protein in developing endosperm of noncultivated Hordeum species with that previously reported for cultivated barley (Hordeum vulgare). As in cultivated barley, the AGPase of H. vulgare subsp. spontaneum and Hordeum murinum endosperm is accounted for by a major extra-plastidial and a minor plastidial isoform. Second, the ratio of ADP-Glc to UDP-Glc was used as an indication of the intracellular location of the AGPase activity in a wide range of starch-synthesizing organs. The ratio is expected to be high in organs in which UDP-Glc and ADP-Glc are synthesized primarily in the cytosol, because the reactions catalyzed by AGPase and UDP-Glc pyrophosphorylase will be coupled and close to equilibrium. This study revealed that ADP-Glc contents and the ratio of ADP-Glc to UDP-Glc were higher in developing graminaceous endosperms than in any other starch-storing organs. Taken as a whole the results indicate that an extra-plastidial AGPase is important in ADP-Glc synthesis in graminaceous endosperms, but not in other starch-storing organs.