Characterization and Localization of Purine Synthesis Enzymes from Soybean Nodules

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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.***//