title: The Klebsiella pneumoniae cytochrome bd' terminal oxidase complex and its role in microaerobic nitrogen fixation.
abstract: Cytochrome bd' has been implicated in having an important role in microaerobic nitrogen fixation in the enteric bacterium Klebsiella pneumoniae, where it is expressed under all conditions that permit diazotrophy. In this paper the sequence of the genes encoding this terminal oxidase (cydAB) of Klebsiella pneumoniae and the characterization of a cyd mutant are reported. The deduced amino acid sequences support the proposal that His 19, His 186 and Met 393 provide three of the four axial ligands to the Fe of the three haems in the oxidase complex. The nitrogen-fixing ability of the mutant was severely impaired in the presence of low concentrations of oxygen compared with the wild-type bacterium. Only the wild-type organism was capable of microaerobic nitrogenase activity supported by fermentation products. It is proposed that formate dehydrogenase-O may be involved in supplying electrons to a respiratory chain terminated by the bd-type oxidase, which would remove inhibitory oxygen and supply ATP for nitrogenase activity.
authors.affiliation: Nitrogen Fixation Laboratory, John Innes Centre, Norwich NR4 7UH, UK.|Department of Biochemistry, University of Southampton, Southampton SO16 7PX, UK.
authors.forename: Navtej S
authors.initials: NS
authors.lastname: Juty
authors.affiliation: Department of Biology, The Johns Hopkinas University, Baltimore, MD 21218, USA.
authors.forename: Farhad
authors.initials: F
authors.lastname: Moshiri
authors.affiliation: Nitrogen Fixation Laboratory, John Innes Centre, Norwich NR4 7UH, UK.
authors.forename: Mike
authors.initials: M
authors.lastname: Merrick
authors.affiliation: Department of Biochemistry, University of Southampton, Southampton SO16 7PX, UK.
authors.forename: Christopher
authors.initials: C
authors.lastname: Anthony
authors.affiliation: Nitrogen Fixation Laboratory, John Innes Centre, Norwich NR4 7UH, UK.
authors.forename: Susan
authors.initials: S
authors.lastname: Hill
mesh_terms: D000332:Aerobiosis; D000595:Amino Acid Sequence; D000693:Anaerobiosis; D003001:Cloning, Molecular; D003573:Cytochrome b Group; D003580:Cytochromes / Q000235:genetics / Q000378:metabolism*; D045222:Electron Transport Chain Complex Proteins; D004734:Energy Metabolism; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D006859:Hydrogen / Q000378:metabolism; D007711:Klebsiella pneumoniae / Q000201:enzymology*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009586:Nitrogen Fixation; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D006859:Hydrogen; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli; D010100:Oxygen