Characterization and Localization of Purine Synthesis Enzymes from Soybean Nodules

在叶绿体中检测到了嘌呤生物合成途径，这表明合成嘌呤的基因可能来自原核或真核生物。此外，初步证据表明，可能存在嘌呤合成反应的同工酶。没有一种合成嘌呤的酶是从植物中提纯到均一的。大豆根瘤是研究植物体内嘌呤合成的一个很好的模式系统，因为这些根瘤通过嘌呤合成将固定的氮吸收到尿囊素和尿囊酸中。因此，与其他植物器官相比，嘌呤合成途径在根瘤中高度表达。这些实验解决了植物中合成嘌呤的几个重要问题。从根瘤中合成嘌呤的两种酶--甘氨酰胺核糖核苷酸转移酶和氨基咪唑核糖核苷酸合成酶--将被提纯和鉴定。这些酶分别催化合成嘌呤的第三步和第五步。使用免疫化学和酶分析，这些酶的分布将在亚细胞，细胞，和整个植物水平。尽管嘌呤在氮代谢中很重要，但人们对植物中的嘌呤合成知之甚少。由嘌呤合成而来的酰脲的生产是向叶和茎提供它们所需的氮源的过程的一部分。这些研究将确定嘌呤生物合成途径的两种酶的特征，并检查负责嘌呤合成的基因的表达和位置。这项研究将提供对植物氮素营养的更好的了解。

The pathway for purine biosynthesis has been detected in plastids which suggests that the genes for purine synthesis may be of prokaryotic or eukaryotic origin. Also, preliminary evidence suggests that there may be isozymes of the purine synthesis reactions. None of the enzymes of purine synthesis have been purified to homogeneity from a plant source. Soybean root nodules are an excellent model system for the study of purine synthesis in plants because these organs assimilate fixed nitrogen into the ureides, allantoin and allantoic acid, via purine synthesis. As a result, the purine synthesis pathway is highly expressed in nodules compared to other plant organs. These experiments address several important problems of purine synthesis in plants. Two enzymes of purine synthesis from nodules, glycinamide ribonucleotide transformylase and aminoimidazole ribonucleotide synthetase, will be purified and characterized. These enzymes catalyze the third and fifth committed steps, respectively, of purine synthesis. Using immunochemical and enzymatic assays, the distribution of these enzymes will be determined at the subcellular, cellular, and whole plant levels.%%% Little is known about purine synthesis in plants despite its importance in nitrogen metabolism. The production of ureides which are derived from purine synthesis is part of the process of supplying leaves and stems with nitrogen source they require. These studies will characterize two of the enzymes of the purine biosynthesis pathway as well as examine the expression and location of the genes responsible for purine synthesis. This research will provide a better understanding of nitrogen nutrition in plants.***//