Ballicora Miguel A, Iglesias Alberto A, Preiss Jack
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA,
Photosynth Res. 2004;79(1):1-24. doi: 10.1023/B:PRES.0000011916.67519.58.
In plants, the synthesis of starch occurs by utilizing ADP-glucose as the glucosyl donor for the elongation of alpha-1,4-glucosidic chains. In photosynthetic bacteria the synthesis of glycogen follows a similar pathway. The first committed step in these pathways is the synthesis of ADP-glucose in a reaction catalyzed by ADP-glucose pyrophosphorylase (ADPGlc PPase). Generally, this enzyme is allosterically regulated by intermediates of the major carbon assimilatory pathway in the respective organism. In oxygenic photosynthesizers, ADPGlc PPase is mainly regulated by 3-phosphoglycerate (activator) and inorganic orthophosphate (inhibitor), interacting in four different patterns. Recent reports have shown that in higher plants, some of the enzymes could also be redox regulated. In eukaryotes, the enzyme is a heterotetramer comprised of two distinct subunits, a catalytic and a modulatory subunit. The latter has been proposed as related to variations in regulation of the enzyme in different plant tissues. Random and site-directed mutagenesis experiments of conserved amino acids revealed important residues for catalysis and regulation. Prediction of the ADPGlc PPase secondary structure suggests that it shares a common folding pattern to other sugar-nucleotide pyrophosphorylases, and they evolved from a common ancestor.
在植物中，淀粉的合成是利用ADP - 葡萄糖作为葡萄糖基供体来延长α-1,4-糖苷链。在光合细菌中，糖原的合成遵循类似的途径。这些途径中的第一个关键步骤是在由ADP - 葡萄糖焦磷酸化酶（ADPGlc PPase）催化的反应中合成ADP - 葡萄糖。一般来说，这种酶受到相应生物体中主要碳同化途径中间产物的变构调节。在产氧光合生物中，ADPGlc PPase主要受3-磷酸甘油酸（激活剂）和无机正磷酸盐（抑制剂）的调节，以四种不同模式相互作用。最近的报道表明，在高等植物中，一些酶也可以受到氧化还原调节。在真核生物中，该酶是由两个不同亚基组成的异源四聚体，一个催化亚基和一个调节亚基。后者被认为与该酶在不同植物组织中的调节变化有关。对保守氨基酸的随机和定点诱变实验揭示了催化和调节的重要残基。ADPGlc PPase二级结构的预测表明，它与其他糖核苷酸焦磷酸化酶具有共同的折叠模式，并且它们是由一个共同的祖先进化而来的。
