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NADH formation by Na + ‐coupled reversed electron transfer in Klebsiella pneumoniae
Author(s) -
PfenningerLi Xiao,
Dimroth Peter
Publication year - 1992
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1992.tb01367.x
Subject(s) - formate dehydrogenase , formate , nad+ kinase , ubiquinol , oxidoreductase , electron transport chain , electron acceptor , nadh dehydrogenase , biology , electron transfer , photochemistry , stereochemistry , biochemistry , chemistry , enzyme , catalysis , cytochrome c , mitochondrion , coenzyme q – cytochrome c reductase , protein subunit , gene
Summary Citrate is fermented by Klebsiella pneumoniae to 2 acetate, 0.5 formate and 1.2 CO 2 . The formation of <1 formate and >1 CO 2 per citrate can be accounted for by the oxidation of formate to CO 2 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 CO 2 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 δμTNa + . The endogenous NADH level of K. pneumoniae cells thus increased in the presence of formate in response to a δpNa + >‐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:ubiqurnone oxidoreductase. The increase of endogenous NADH was dependent on the δpNa + 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;μTNa + of about 120 mV consisting of δpNa + of 60 mV and ΔΨ of the same magnitude. Neither the δpNa + nor the ΔΨ 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. It is suggested that NADH formation by reversed δμTNa + ‐coupled electron transfer in these cells is an essential requirement for the synthesis of cell material from citrate.