Abstract
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 language | English |
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Pages (from-to) | 557-563 |
Number of pages | 7 |
Journal | Biochemical Journal |
Volume | 317 |
Issue number | 2 |
DOIs | |
Publication status | Published - 15 Jul 1996 |
Keywords
- 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