pH dependence of the function of sodium ion extrusion systems in Escherichia coli.
pH dependence of the function of sodium ion extrusion systems in Escherichia coli.
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DOI：
10.1016/s0005-2728(97)00102-3
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发表时间：
1998-03
期刊：
影响因子：
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通讯作者：
Tatsuya Sakuma;Naomi Yamada;H. Saito;T. Kakegawa;Hiroshi Kobayashi
中科院分区：
文献类型：
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作者：
Tatsuya Sakuma;Naomi Yamada;H. Saito;T. Kakegawa;Hiroshi Kobayashi
大肠杆菌有三个钠离子挤出系统，NhaA，NhaB和ChaA。在本研究中，我们使用具有这些转运蛋白之一的突变体来研究pH对这些转运蛋白功能的影响，发现（1）具有NhaB的突变体在pH 7.5下排出钠离子，但在pH 8.5下不排出钠离子，（2）在pH 7.5和8.5下都观察到来自具有ChaA的突变体细胞的钠离子流出，但在pH 7.5下活性较低，和（3）在pH6.5至8.5下，钠离子从具有NhaA的突变体细胞中排出。具有NhaA的细胞的挤出活性高于具有NhaB或ChaA的细胞。这些结果表明NhaB在低于8的pH下起作用，而ChaA主要在高于8的碱性pH下挤出钠离子。有人还建议，活性的NhaB和ChaA是不够的，以保持低水平的内部钠离子时，外部浓度的钠离子是高的，和NhaA是诱导在一个广泛的范围内的介质pH值在这样的条件下。
Escherichia coli has three systems for sodium ion extrusion, NhaA, NhaB and ChaA. In this study, we examined the effect of pH on the function of these transporters using mutants having one of them, and found that (1) a mutant having NhaB excreted sodium ions at pH 7.5 but not at pH 8.5, (2) the efflux of sodium ions from mutant cells having ChaA was observed at both pH 7.5 and 8.5, but the activity was lower at pH 7.5, and (3) sodium ions were excreted from mutant cells having NhaA at pH 6.5 to 8.5. The extrusion activity of cells having NhaA was higher than that of cells having NhaB or ChaA. These results indicate that NhaB functions at a pH below 8, and ChaA extrudes sodium ions mainly at an alkaline pH above 8. It was also suggested that the activity of NhaB and ChaA is not enough to maintain a low level of internal sodium ions when the external concentration of sodium ions is high, and NhaA is induced within a wide range of medium pH under such conditions.