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Oxidant-induced formation of a neutral flavosemiquinone in the Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from Vibrio cholerae


Tao, M; Casutt, M S; Fritz, G; Steuber, J (2008). Oxidant-induced formation of a neutral flavosemiquinone in the Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from Vibrio cholerae. Biochim. Biophys. Acta: Bioenergetics, 1777(7-8):696-702.

Abstract

The Na+ -translocating NADH:quinone oxidoreductase Na+-NQR) from the human pathogen Vibrio cholerae is a respiratory flavo-FeS complex composed of the six subunits NqrA-F. The Na+-NQR was produced as His6-tagged protein by homologous expression in V. cholerae. The isolated complex contained near stoichiometric amounts of non-covalently bound FAD (0.78 mol/mol Na+-NQR) and riboflavin (0.70 mol/mol Na+-NQR), catalyzed NADH-driven Na+ transport (40 nmol Na+ min-1 mg-1), and was inhibited by 2-n-heptyl-4-hydroxyquinoline-N-oxide. EPR spectroscopy showed that Na+-NQR as isolated contained very low amounts of a neutral flavosemiquinone (10-3 mol/mol Na+-NQR). Reduction with NADH resulted in the formation of an anionic flavosemiquinone (0.10 mol/mol Na+-NQR). Subsequent oxidation of the Na+-NQR with ubiquinone-1 or O2 led to the formation of a neutral flavosemiquinone (0.24 mol/mol Na+-NQR). We propose that the Na+-NQR is fully oxidized in its resting state, and discuss putative schemes of ADH-triggered redox transitions.

Abstract

The Na+ -translocating NADH:quinone oxidoreductase Na+-NQR) from the human pathogen Vibrio cholerae is a respiratory flavo-FeS complex composed of the six subunits NqrA-F. The Na+-NQR was produced as His6-tagged protein by homologous expression in V. cholerae. The isolated complex contained near stoichiometric amounts of non-covalently bound FAD (0.78 mol/mol Na+-NQR) and riboflavin (0.70 mol/mol Na+-NQR), catalyzed NADH-driven Na+ transport (40 nmol Na+ min-1 mg-1), and was inhibited by 2-n-heptyl-4-hydroxyquinoline-N-oxide. EPR spectroscopy showed that Na+-NQR as isolated contained very low amounts of a neutral flavosemiquinone (10-3 mol/mol Na+-NQR). Reduction with NADH resulted in the formation of an anionic flavosemiquinone (0.10 mol/mol Na+-NQR). Subsequent oxidation of the Na+-NQR with ubiquinone-1 or O2 led to the formation of a neutral flavosemiquinone (0.24 mol/mol Na+-NQR). We propose that the Na+-NQR is fully oxidized in its resting state, and discuss putative schemes of ADH-triggered redox transitions.

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Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Department of Biochemistry
07 Faculty of Science > Department of Biochemistry
Dewey Decimal Classification:570 Life sciences; biology
Language:English
Date:July 2008
Deposited On:23 Sep 2008 07:14
Last Modified:05 Apr 2016 12:28
Publisher:Elsevier
ISSN:0005-2728
Publisher DOI:https://doi.org/10.1016/j.bbabio.2008.04.006
PubMed ID:18454933

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