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J Biol Chem. 2003 Jul 18;278(29):26817-22. Epub 2003 May 10.

The C-terminally truncated NuoL subunit (ND5 homologue) of the Na+-dependent complex I from Escherichia coli transports Na+.

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  • 1Mikrobiologisches Institut der Eidgenössischen Technischen Hochschule, ETH-Zentrum, Schmelzbergstrasse 7, CH-8092 Zürich, Switzerland.


The NADH:quinone oxidoreductase (complex I) from Escherichia coli acts as a primary Na+ pump. Expression of a C-terminally truncated version of the hydrophobic NuoL subunit (ND5 homologue) from E. coli complex I resulted in Na+-dependent growth inhibition of the E. coli host cells. Membrane vesicles containing the truncated NuoL subunit (NuoLN) exhibited 2-4-fold higher Na+ uptake activity than control vesicles without NuoLN. Respiratory proton transport into inverted vesicles containing NuoLN decreased upon addition of Na+, but was not affected by K+, indicating a Na+-dependent increase of proton permeability of membranes in the presence of NuoLN. The His-tagged NuoLN protein was solubilized, enriched by affinity chromatography, and reconstituted into proteoliposomes. Reconstituted His6-NuoLN facilitated the uptake of Na+ into the proteoliposomes along a concentration gradient. This Na+ uptake was prevented by EIPA (5-(N-ethyl-N-isopropyl)-amiloride), which acts as inhibitor against Na+/H+ antiporters.

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