Are enzymes of the oxidative limb of the Pentose Phosphate Pathway in soybean nodules organized in a macro molecular complex?

9407122 Kohl大豆根瘤细胞质中戊糖磷酸途径（PPP）的氧化分支可能是核糖-5-磷酸的重要来源，核糖-5-磷酸是合成尿素的起点，也是生物固定氮从根瘤输出到整个植物的形式。 大豆的结果表明，根瘤提取物中的葡萄糖-6-磷酸（G6 P）与散装培养基中的G6 P浓度不平衡，并且PPP活性的一半在相对适度的离心力（290，000 x g）下沉淀，这导致PPP作为大分子复合物（代谢物）发挥作用的命题。 在这种代谢子中，PPP中间体从一种酶传递到下一种酶。 在其他系统中的代谢通道的例子已被证明是重要的保存有限的溶剂容量的细胞水，保护中间体是不稳定的，如果没有酶结合，并保持代谢物浓度梯度内细胞。 如果我们关于PPP通道的假设是正确的，那么这个“通道”的例子不仅有助于理解结核代谢，而且有助于理解其他植物和动物细胞中的戊糖磷酸代谢。 将使用几种方法来研究PPP通道的想法，包括（i）确定哪些PPP中间体与其在本体介质中的对应物不平衡，（ii）通过其离心和凝胶过滤行为测量“代谢子”大小，以及（iii）比较代谢子与解离酶的“集合”的途径功能的动力学。 %代谢途径由一系列反应组成，每个反应由特定的酶催化。 一个反应的产物成为下一个酶的底物（食物），直到形成最终产物。 在某些情况下，一个途径的酶相互关联，使得一个反应的产物不会离开“形成”的位点。这样，产物可以直接从一种酶“引导”到另一种酶。 当这种情况发生时，通道效应可以通过加速一系列反应和保护某些不稳定的中间体来提高代谢效率。 在这个实验室的工作已经导致的假设，戊糖磷酸途径的酶，在碳水化合物的形成的关键途径，作为一个大分子复合物的通道中间体从一个酶到下一个。 目前的工作将测试这一想法，并添加到身体的证据表明，类似的酶的安排也发生在其他细胞的代谢途径。 ***

9407122 Kohl The oxidative limb of the pentose phosphate pathway (PPP) in the cytoplasm of soybean nodules may be an important source of ribose- 5-phosphate, the starting point for the synthesis of ureades and the form in which biologically fixed nitrogen is exported from the nodule to the whole plant. Results with soybean suggesting that glucose-6-phosphate (G6P) in nodule extract is not in equilibrium with the concentration of G6P in bulk medium, and that half of the PPP activity precipitates at a relatively modest centrifugal force (290,000 x g) have led to the proposition that the PPP functions as a macromolecular complex (metabolon). Within this metabolon, PPP intermediates are channeled from one enzyme to the next. Examples of metabolic channeling in other systems has proved to be important in conserving the limited solvent capacity of cell water, protecting intermediates which are unstable if not enzyme bound, and maintaining metabolite concentration gradients inside cells. If our hypothesis is correct about PPP channeling, this example of "channeling" would contribute not only to understanding about nodule metabolism but also to understanding pentose phosphate metabolism in other plant and animal cells. Several approaches will be used to investigate the idea of PPP channeling including (i) determining which PPP intermediates are out of equilibrium with their counterparts in the bulk medium, (ii) measuring "metabolon" size via its centrifugal and gel filtration behavior, and (iii) comparing the kinetics of pathway function by metabolons vs. "collections" of dissociated enzymes. %%% Metabolic pathways consist of a series of reactions, each catalyzed by a specific enzyme. The product of one reaction becomes the substrate (food) of the next enzyme until a final product is formed. In some cases, the enzymes of a pathway are associated with each other such that the product of one reaction does not leave the site of "formation." In this way product(s) m ay be "channeled" directly from one enzyme to another. When this happens, channeling can be important in improving metaboliic efficiency by speeding up a series of reactions and protecting certain unstable intermediates on the way to a final product. Work in this laboratory has led to the hypothesis that enzymes of the pentose phosphate pathway, a key pathway in carbohydrate formation, operates as a macromolecular complex to channel intermediates from one enzyme to the next. The present work will test this idea and add to the body of evidence that similar enzyme arrangements occur in the metabolic pathways of other cells as well. ***