Department of Molecular Biology and Plant Physiology, University of Aarhus, DK-8000 Aarhus C, Denmark.
Plant Physiol. 1983 May;72(1):56-9. doi: 10.1104/pp.72.1.56.
Soybean (Glycine max) and pea (Pisum sativum) differ in the transport of fixed nitrogen from nodules to shoots. The dominant nitrogen transport compounds for soybean are ureides, while amides dominate in pea. A possible enzymic basis for this difference was examined.The level of enzymes involved in the formation of the ureides allantoin and allantoic acid from inosine 5'-monophosphate (IMP) was compared in different tissues of pea and soybean. Two enzymes, 5'-nucleotidase and uricase, from soybean nodules were found to be 50- and 25-fold higher, respectively, than the level found in pea nodules. Other purine catabolizing enzymes (purine nucleosidase, xanthine dehydrogenase, and allantoinase) were found to be at the same level in the two species. From comparison of enzyme activities in nodules with those from roots, stems, and leaves, two enzymes were found to be nodule specific, namely uricase and xanthine dehydrogenase. The level of enzymes found in the bacteroids indicated no significant contribution of Rhizobium japonicum purine catabolism in the overall formation of ureides in the soybean nodule. The presence in the nodules of purine nucleosidase and ribokinase activities makes a recirculation of the ribose moiety possible. In concert with phosphoribosylpyrophosphate synthetase, ribose becomes available for a new round of purine de novo synthesis, and thereby ureide formation.
大豆（Glycine max）和豌豆（Pisum sativum）在从根瘤向地上部运输固定氮方面存在差异。大豆中主要的氮运输化合物是尿囊素，而在豌豆中酰胺占主导地位。为此差异，我们对可能的酶学基础进行了研究。比较了不同组织中 pea 和 soybean 中肌苷 5'-单磷酸 (IMP) 形成尿囊素和尿囊酸的酶的水平。发现大豆根瘤中的两种酶，5'-核苷酸酶和尿酸酶，分别比豌豆根瘤中的水平高 50 倍和 25 倍。其他嘌呤分解代谢酶（嘌呤核苷酶、黄嘌呤脱氢酶和尿囊素酶）在两种物种中的水平相同。通过比较根瘤中的酶活性与根、茎和叶中的酶活性，发现有两种酶是根瘤特有的，即尿酸酶和黄嘌呤脱氢酶。在类菌体中发现的酶水平表明，根瘤菌在大豆根瘤中尿囊素的整体形成过程中没有显著贡献嘌呤分解代谢。嘌呤核苷酶和核酮糖激酶活性的存在使得核糖部分的再循环成为可能。与磷酸核糖焦磷酸合成酶一起，核糖可用于新的嘌呤从头合成循环，从而形成尿囊素。
