title: Characterisation of Escherichia coli K-12 mutants defective in formate-dependent nitrite reduction: essential roles for hemN and the menFDBCE operon.
abstract: Three Escherichia coli mutants defective in formate-dependent nitrite reduction (Nrf activity) were characterised. Two of the mutants, JCB354 and JCB356, synthesized all five c-type cytochromes previously characterised in anaerobic cultures of E. coli. The third mutant, JCB355, was defective for both cytochrome b and cytochrome c synthesis, but only during anaerobic growth. The insertion sites of the transposon in strains JCB354 and JCB356 mapped to the menFDBCE operon; the hemN gene was disrupted in strain JCB355. The mutation in strain JCB354 was complemented by a plasmid encoding only menD; strain JCB356 was complemented by a plasmid encoding only menBCE. A mutant defective in the methyltransferase activity involved in both ubiquinone synthesis and conversion of demethylmenaquinone to menaquinone expressed the same Nrf activity as the parental strain. The effects of men, ubiA and ubiE mutations on other cytochrome-c-dependent electron transfer pathways were also determined. The combined data establish that menaquinones are essential for cytochrome-c-dependent trimethylamine-N-oxide reductase (Tor) and Nrf activity, but that either menaquinone or ubiquinone, but not demethylmenaquinone, can transfer electrons to a third cytochrome-c-dependent electron transfer chain, the periplasmic nitrate reductase.
authors.affiliation: School of Biochemistry, University of Birmingham, Birmingham B15 2TT, UK.
authors.forename: K
authors.initials: K
authors.lastname: Tyson
authors.forename: R
authors.initials: R
authors.lastname: Metheringham
authors.forename: L
authors.initials: L
authors.lastname: Griffiths
authors.forename: J
authors.initials: J
authors.lastname: Cole
mesh_terms: D000693:Anaerobiosis; D003573:Cytochrome b Group / Q000032:analysis; D003574:Cytochrome c Group / Q000096:biosynthesis; D004579:Electron Transport; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005561:Formates / Q000378:metabolism*; D005990:Glycerol / Q000378:metabolism; D006418:Heme / Q000096:biosynthesis; D008780:Methyltransferases / Q000235:genetics; D009154:Mutation; D009285:Naphthoquinones / Q000378:metabolism; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D009876:Operon; D010084:Oxidation-Reduction; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D014812:Vitamin K / Q000096:biosynthesis
chemical_list: D003573:Cytochrome b Group; D003574:Cytochrome c Group; D029968:Escherichia coli Proteins; D005561:Formates; D009285:Naphthoquinones; D009573:Nitrites; C083951:cytochrome c553; C030544:formic acid; D014812:Vitamin K; D006418:Heme; C022302:cytochrome C-552; D010089:Oxidoreductases, N-Demethylating; C023186:trimethylamine dehydrogenase; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D008780:Methyltransferases; C104639:UbiE protein, E coli; D005990:Glycerol