Moran J F, Iturbe-Ormaetxe I, Matamoros M A, Rubio M C, Clemente M R, Brewin N J, Becana M
Departamento de Nutrición Vegetal, Estación Experimental de Aula Dei, Consejo Superior de Investigaciones Científicas, Apdo 202, 50080 Zaragoza, Spain.
Plant Physiol. 2000 Nov;124(3):1381-92. doi: 10.1104/pp.124.3.1381.
The thiol tripeptides glutathione (GSH) and homoglutathione (hGSH) are very abundant in legume root nodules and their synthesis is catalyzed by the enzymes gamma-glutamylcysteine synthetase (gammaECS), GSH synthetase (GSHS), and hGSH synthetase (hGSHS). As an essential step to elucidate the role of thiols in N(2) fixation we have isolated cDNAs encoding the three enzymes and have quantified the transcripts in nodules. Assay of enzyme activities in highly purified nodule organelles revealed that gammaECS is localized in the plastids, hGSHS in the cytosol, and GSHS in the cytosol and mitochondria. These results are consistent with sequence analyses. Subcellular fractionation of nodules also showed that bacteroids contain high thiol concentrations and high specific gammaECS and GSHS activities. Results emphasize the role of nodule plastids in antioxidant protection and in control of thiol synthesis, and suggest that plastids may be important in the stress response of nodules. Overall, our results provide further evidence that thiol synthesis is critical for nodule functioning.
硫醇三肽谷胱甘肽（GSH）和高半胱甘肽（hGSH）在豆科植物根瘤中含量极为丰富，它们的合成由γ-谷氨酰半胱氨酸合成酶（γECS）、谷胱甘肽合成酶（GSHS）和高半胱甘肽合成酶（hGSHS）催化。作为阐明硫醇在固氮作用中角色的关键步骤，我们已分离出编码这三种酶的cDNA，并对根瘤中的转录本进行了定量分析。对高度纯化的根瘤细胞器中的酶活性测定表明，γECS定位于质体中，hGSHS定位于细胞质中，而GSHS则定位于细胞质和线粒体中。这些结果与序列分析一致。根瘤的亚细胞分级分离还表明，类菌体含有高浓度的硫醇以及高特异性的γECS和GSHS活性。结果强调了根瘤质体在抗氧化保护和硫醇合成控制中的作用，并表明质体在根瘤的应激反应中可能很重要。总体而言，我们的结果进一步证明了硫醇合成对根瘤功能至关重要。
