Different physiological roles of two independent pathways for nitrite reduction to ammonia by enteric bacteria
Different physiological roles of two independent pathways for nitrite reduction to ammonia by enteric bacteria
复制标题
肠道细菌将亚硝酸盐还原为氨的两种独立途径的不同生理作用
作者：
L. Page;L. Griffiths;J. Cole
操纵子融合菌株和突变体的大肠杆菌K-12缺乏NADH依赖的亚硝酸盐还原酶已被用来确定两个独立的途径亚硝酸盐还原成氨的调节和生理作用。甲酸盐和NADH依赖的途径（NRF和Nir，分别）在有氧生长过程中被完全抑制，在无亚硝酸盐的厌氧生长过程中部分活跃，并进一步诱导亚硝酸盐厌氧。两者都依赖于功能性Fnr蛋白（无氧呼吸基因的转录激活因子）。在厌氧生长过程中，在硝酸盐的存在下，Nir途径被完全诱导，但NRF强烈抑制。突变体缺陷的NarL蛋白，诱导硝酸还原酶基因的转录，但抑制延胡索酸还原酶基因在硝酸盐的存在下，被derepressed的NRF活性在生长过程中与硝酸盐，但NIR酶活性较低。NRF组件的合成也是敏感的葡萄糖阻遏和弱激活NarL在生长过程中，在没有硝酸盐。这些数据表明，Nir途径提供了一种机制，用于解毒在细胞质中形成的亚硝酸盐作为硝酸盐还原的产物。相反，由Nrf途径的亚硝酸盐的产电还原在厌氧生长期间提供了第二能量来源，并且因此当在生物学上更有利的电子受体硝酸盐可用时被NarL蛋白抑制。在已知被NarL蛋白激活或抑制的操纵子的启动子中发现了两个短的DNA序列，5′-TACCAT-3′和5′-CTCCTT-3′。据推测，NarL通过与位于RNA聚合酶结合位点5′端的这些序列中的一个或两个结合来激活nir B转录，但通过与转录起始点附近结合来抑制其他操纵子，包括nrf。
Operon fusion strains and mutants of Escherichia coli K-12 lacking the NADH-dependent nitrite reductase have been used to determine the regulation and physiological roles of two independent pathways for nitrite reduction to ammonia. Both the formate-and NADH-dependent pathways (Nrf and Nir, respectively) were totally repressed during aerobic growth, partially active during anaerobic growth in the absence of nitrite and further induced anaerobically by nitrite. Both were dependent upon a functional Fnr protein (a transcription activator of genes for anaerobic respiration). During anaerobic growth in the presence of nitrate, the Nir pathway was fully induced but Nrf was strongly repressed. Mutants defective in the NarL protein, which induces transcription of nitrate reductase genes but represses fumarate reductase genes in the presence of nitrate, were derepressed for Nrf activity during growth with nitrate, but the Nir enzyme was less active. The synthesis of Nrf components was also sensitive to glucose repression and weak activation by NarL during growth in the absence of nitrate. These data indicate that the Nir pathway provides a mechanism for detoxifying nitrite formed in the cytoplasm as a product of nitrate reduction. In contrast, the electrogenic reduction of nitrite by the Nrf pathway provides a secondary source of energy during anaerobic growth and is consequently repressed by the NarL protein when the thermodynamically more favourable electron acceptor, nitrate, is available. Two short DNA sequences, 5′-TACCAT-3′ and 5′-CTCCTT-3′, were found in the promoters of operons known to be activated or repressed by the NarL protein. It is proposed that NarL activates nir B transcription by binding to one or both of these sequences located 5′ to the RNA polymerase binding site, but represses other operons, including nrf, by binding close to the transcription start.
narL 基因产物激活大肠杆菌中的硝酸还原酶操纵子并抑制富马酸还原酶和三甲胺 N-氧化物还原酶操纵子。
DOI：
10.1073/pnas.84.11.3901
发表时间：
1987
影响因子：
11.1
作者：
Iuchi,S;Lin,EC
通讯作者：
Lin,EC
Fnr 和 NarL 调节所需的大肠杆菌 nar 启动子中序列的位置。
DOI：
--
发表时间：
1988
期刊：
The Journal of biological chemistry
影响因子：
--
作者：
Li,SF;DeMoss,JA
通讯作者：
DeMoss,JA
增强子结合蛋白的可逆磷酸化调节细菌氮利用基因的转录。
影响因子：
13.8
作者：
Magasanik,B
通讯作者：
Magasanik,B