Estación Experimental del Zaidín, CSIC, PO Box 419, 18080 Granada, Spain.
Biochem Soc Trans. 2011 Dec;39(6):1880-5. doi: 10.1042/BST20110732.
Nitric oxide (NO) is a gaseous signalling molecule which becomes very toxic due to its ability to react with multiple cellular targets in biological systems. Bacterial cells protect against NO through the expression of enzymes that detoxify this molecule by oxidizing it to nitrate or reducing it to nitrous oxide or ammonia. These enzymes are haemoglobins, c-type nitric oxide reductase, flavorubredoxins and the cytochrome c respiratory nitrite reductase. Expression of the genes encoding these enzymes is controlled by NO-sensitive regulatory proteins. The production of NO in rhizobia-legume symbiosis has been demonstrated recently. In functioning nodules, NO acts as a potent inhibitor of nitrogenase enzymes. These observations have led to the question of how rhizobia overcome the toxicity of NO. Several studies on the NO response have been undertaken in two non-dentrifying rhizobial species, Sinorhizobium meliloti and Rhizobium etli, and in a denitrifying species, Bradyrhizobium japonicum. In the present mini-review, current knowledge of the NO response in those legume-associated endosymbiotic bacteria is summarized.
一氧化氮（NO）是一种气态信号分子，由于其能够与生物系统中的多个细胞靶标反应，因此变得非常有毒。细菌细胞通过表达能够将该分子氧化为硝酸盐、还原为亚硝酸盐或氨的解毒酶来抵御 NO。这些酶是血红蛋白、c 型一氧化氮还原酶、风味还原酶和细胞色素 c 呼吸亚硝酸盐还原酶。这些酶的基因表达受 NO 敏感调节蛋白控制。最近已经证明根瘤菌-豆科植物共生体中会产生 NO。在功能正常的根瘤中，NO 作为氮酶的有效抑制剂。这些观察结果引发了一个问题，即根瘤菌如何克服 NO 的毒性。在两种非固氮根瘤菌（Sinorhizobium meliloti 和 Rhizobium etli）和一种脱氮菌（Bradyrhizobium japonicum）中进行了几项关于 NO 反应的研究。在本综述中，总结了与豆科植物相关的内共生细菌中 NO 反应的最新知识。
