CLARiTY 17 UV/Vis用于“大腸桿菌的NADH依賴(lài)亞硝酸還原酶Nir在發(fā)酵氨化中的作用”

CLARiTY 17 UV/Vis用于“大腸桿菌的NADH依賴(lài)亞硝酸還原酶Nir在發(fā)酵氨化中的作用”

The role of the NADH-dependent nitrite reductase, Nir, from Escherichia coli in fermentative ammonification

了解每種參與還原酶的特定作用對(duì)于描述決定細(xì)胞對(duì)其環(huán)境的反應(yīng)的生化平衡是必要的,硝酸鹽和亞硝酸鹽還原對(duì)于氮同化和無(wú)氧代謝至關(guān)重要。大腸桿菌中的可溶性細(xì)胞質(zhì)siroheme NADH-亞硝酸還原酶(Nir)是硝酸鹽/亞硝酸鹽同化所必需的,但也有報(bào)道要么“解毒”亞硝酸鹽,要么進(jìn)行發(fā)酵氨化以支持厭氧分解代謝。從理論上講,亞硝酸鹽解毒對(duì)于硝酸鹽的厭氧生長(zhǎng)很重要,在此期間過(guò)量的亞硝酸鹽會(huì)被還原成銨。 Nir的發(fā)酵氨化對(duì)于在亞硝酸鹽存在下的厭氧生長(zhǎng)期間非呼吸ATP產(chǎn)生的最大化是重要的。本文報(bào)道的實(shí)驗(yàn)旨在通過(guò)在限定培養(yǎng)基中厭氧條件下培養(yǎng)大腸桿菌以及缺乏Nir或呼吸亞硝酸還原酶(Nrf)的突變菌株,同時(shí)監(jiān)測(cè)氮利用和發(fā)酵代謝物,來(lái)測(cè)試Nir在發(fā)酵氨化中的潛在作用。為了關(guān)注Nir在發(fā)酵氨化中的作用,在大多數(shù)實(shí)驗(yàn)中使用pH控制來(lái)消除由于硝酸形成引起的亞硝酸鹽毒性。我們的研究結(jié)果表明,Nir在發(fā)酵生長(zhǎng)期間具有顯著的益處,反映了發(fā)酵氨化而不是解毒。我們得出結(jié)論,Nir的發(fā)酵氨化允許葡萄糖在能量上有利地發(fā)酵成甲酸鹽和乙酸鹽。根據(jù)Nir在其他細(xì)菌和植物中的作用,討論了這些結(jié)果和結(jié)論。

Nitrate and nitrite reduction are of paramount importance for nitrogen assimilation and anaerobic metabolism, and understanding the specific roles of each participating reductase is necessary to describe the biochemical balance that dictates cellular responses to their environments. The soluble, cytoplasmic siroheme NADH-nitrite reductase (Nir) in?Escherichia coli?is necessary for nitrate/nitrite assimilation but has also been reported to either “detoxify” nitrite, or to carry out fermentative ammonification in support of anaerobic catabolism. Theoretically, nitrite detoxification would be important for anaerobic growth on nitrate, during which excess nitrite would be reduced to ammonium. Fermentative ammonification by Nir would be important for maximization of non-respiratory ATP production during anaerobic growth in the presence of nitrite. Experiments reported here were designed to test the potential role of Nir in fermentative ammonification directly by growing?E. coli?along with mutant strains lacking Nir or the respiratory nitrite reductase (Nrf) under anaerobic conditions in defined media while monitoring nitrogen utilization and fermentation metabolites. To focus on the role of Nir in fermentative ammonification, pH control was used in most experiments to eliminate nitrite toxicity due to nitric acid formation. Our results demonstrate that Nir confers a significant benefit during fermentative growth that reflects fermentative ammonification rather than detoxification. We conclude that fermentative ammonification by Nir allows for the energetically favorable fermentation of glucose to formate and acetate. These results and conclusions are discussed in light of the roles of Nir in other bacteria and in plants.


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