title: NADH formation by Na(+)-coupled reversed electron transfer in Klebsiella pneumoniae.
abstract: Citrate is fermented by Klebsiella pneumoniae to 2 acetate, 0.5 formate and 1.2 CO2. The formation of less than 1 formate and greater than 1 CO2 per citrate can be accounted for by the oxidation of formate to CO2 in order to provide reducing equivalents for the assimilation of citrate into cell carbon. A membrane-bound electron transport chain is apparently involved in NADH synthesis by these cells. The electrons from formate oxidation to CO2 are used to reduce ubiquinone to ubiquinol by membrane-bound formate dehydrogenase and ubiquinol further delivers its electrons to NAD+, if this endergonic reaction is powered by delta mu Na+. The endogenous NADH level of K. pneumoniae cells thus increased in the presence of formate in response to a delta pNa+ greater than -100 mV. NADH formation was completely abolished in the presence of oxygen or after addition of hydroxyquinoline-N-oxide, a specific inhibitor of the Na(+)-translocating NADH:ubiquinone oxidoreductase. The increase of endogenous NADH was dependent on the delta pNa+ applied to the cells. Inverted membrane vesicles of K. pneumoniae catalysed the reduction of NAD+ to NADH with formate as electron donor after application of delta mu Na+ of about 120 mV consisting of delta pNa+ of 60 mV and delta psi of the same magnitude. Neither the delta pNa+ nor the delta psi of this size alone was sufficient to drive the endergonic reaction. Strictly anaerobic conditions were required for NADH formation and hydroxyquinoline-N-oxide completely inactivated the reaction.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Mikrobiologisches Institut, Eidgenössische Technische Hochschule, ETH-Zentrum, Zurich, Switzerland.
authors.forename: X D
authors.initials: XD
authors.lastname: Pfenninger-Li
authors.forename: P
authors.initials: P
authors.lastname: Dimroth
mesh_terms: D002951:Citrates / Q000378:metabolism; D019343:Citric Acid; D004579:Electron Transport / Q000502:physiology*; D042967:Electron Transport Complex I; D005285:Fermentation / Q000502:physiology; D005561:Formates / Q000378:metabolism; D007711:Klebsiella pneumoniae / Q000378:metabolism*; D009243:NAD / Q000378:metabolism*; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D010084:Oxidation-Reduction; D012964:Sodium / Q000378:metabolism*
chemical_list: D002951:Citrates; D005561:Formates; D009243:NAD; C030544:formic acid; D019343:Citric Acid; D012964:Sodium; D009247:NADH, NADPH Oxidoreductases; D042967:Electron Transport Complex I