Nark is a nitrite-extrusion system involved in anaerobic nitrate respiration by Escherichia coli |
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| Authors: | John J. Rowe,Trees Ubbink-Kok,Douwe Molenaar,&dagger ,Wil N. Konings,Arnold J. M. Driessen |
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| Affiliation: | Department of Biology, University of Dayton, Dayton, Ohio 45469-2320, USA.;Department of Microbiology, University of Groningen, 9751 NN Haren, The Netherlands. |
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| Abstract: | Escherichia coli can use nitrate as a terminal electron acceptor for anaerobic respiration. A polytopic membrane protein, termed NarK, has been implicated in nitrate uptake and nitrite excretion and is thought to function as a nitrate/nitrite antiporter. The longest-lived radioactive isotope of nitrogen, 13N-nitrate (half-life = 9.96 min) and the nitrite-sensitive fluorophore N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide have now been used to define the function of NarK. At low concentrations of nitrate, NarK mediates the electrogenic excretion of nitrite rather than nitrate/nitrite exchange. This process prevents intracellular accumulation of toxic levels of nitrite and allows further detoxification in the periplasm through the action of nitrite reductase. |
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