Structural investigation of the molybdenum site of the periplasmic nitrate reductase from Thiosphaera pantotropha by X-ray absorption spectroscopy

B Bennett, J M Charnock, H J Sears, B C Berks, A J Thomson, S J Ferguson, C D Garner, D J Richardson

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The molybdenum centre of the periplasmic respiratory nitrate reductase from the denitrifying bacterium Thiosphaera pantotropha has been probed using molybdenum K-edge X-ray absorption spectroscopy. The optimum fit of the Mo(VI) EXAFS suggests two ==O, three -S- and either a fourth -S- or an -O-/-N- as molybdenum ligands in the ferricyanide-oxidized enzyme. Three of the -S- ligands are proposed to be the two sulphur atoms of the molybdopterin dithiolene group and Cys-181. Comparison of the EXAFS of the ferricyanide-oxidized enzyme with that of a nitrate-treated sample containing 30% Mo(V) suggests that the Mo(VI)-->Mo(V) reduction is accompanied by conversion of one ==O to -O-. The best fit to the Mo(IV) EXAFS of dithionite-reduced enzyme was obtained using one ==O, one -O- and four -S-/-Cl ligands. The periplasmic nitrate reductase molybdenum co-ordination environment in both the Mo(VI) and Mo(IV) oxidation states is distinct from that found in the membrane-bound respiratory nitrate reductase.

Original languageEnglish
Pages (from-to)557-563
Number of pages7
JournalBiochemical Journal
Issue number2
Publication statusPublished - 15 Jul 1996



  • Amino Acid Sequence
  • Ferricyanides
  • Fourier Analysis
  • Gram-Negative Chemolithotrophic Bacteria
  • Ligands
  • Metalloproteins
  • Models, Chemical
  • Molecular Sequence Data
  • Molybdenum
  • Nitrate Reductase
  • Nitrate Reductases
  • Nitrates
  • Oxidation-Reduction
  • Sequence Homology, Amino Acid
  • Spectrum Analysis
  • X-Rays
  • Comparative Study
  • Journal Article
  • Research Support, Non-U.S. Gov't

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