title: Quinone reduction by the Na+-translocating NADH dehydrogenase promotes extracellular superoxide production in Vibrio cholerae.
abstract: The pathogenicity of Vibrio cholerae is influenced by sodium ions which are actively extruded from the cell by the Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR). To study the function of the Na(+)-NQR in the respiratory chain of V. cholerae, we examined the formation of organic radicals and superoxide in a wild-type strain and a mutant strain lacking the Na(+)-NQR. Upon reduction with NADH, an organic radical was detected in native membranes by electron paramagnetic resonance spectroscopy which was assigned to ubisemiquinones generated by the Na(+)-NQR. The radical concentration increased from 0.2 mM at 0.08 mM Na(+) to 0.4 mM at 14.7 mM Na(+), indicating that the concentration of the coupling cation influences the redox state of the quinone pool in V. cholerae membranes. During respiration, V. cholerae cells produced extracellular superoxide with a specific activity of 10.2 nmol min(-1) mg(-1) in the wild type compared to 3.1 nmol min(-1) mg(-1) in the NQR deletion strain. Raising the Na(+) concentration from 0.1 to 5 mM increased the rate of superoxide formation in the wild-type V. cholerae strain by at least 70%. Rates of respiratory H(2)O(2) formation by wild-type V. cholerae cells (30.9 nmol min(-1) mg(-1)) were threefold higher than rates observed with the mutant strain lacking the Na(+)-NQR (9.7 nmol min(-1) mg(-1)). Our study shows that environmental Na(+) could stimulate ubisemiquinone formation by the Na(+)-NQR and hereby enhance the production of reactive oxygen species formed during the autoxidation of reduced quinones.
authors.affiliation: Biochemisches Institut, Universität Zürich, CH-8057 Zürich, Switzerland.
authors.forename: Po-Chi
authors.initials: PC
authors.lastname: Lin
authors.forename: Karin
authors.initials: K
authors.lastname: Türk
authors.forename: Claudia C
authors.initials: CC
authors.lastname: Häse
authors.forename: Günter
authors.initials: G
authors.lastname: Fritz
authors.forename: Julia
authors.initials: J
authors.lastname: Steuber
mesh_terms: D016227:Benzoquinones / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport / Q000502:physiology; D017353:Gene Deletion; D011808:Quinone Reductases / Q000235:genetics / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*; D014734:Vibrio cholerae / Q000201:enzymology* / Q000235:genetics
chemical_list: D016227:Benzoquinones; D017382:Reactive Oxygen Species; D013481:Superoxides; C004532:quinone; D012964:Sodium; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases