Characterisation of [Cu4S], the catalytic site in nitrous oxide reductase, by EPR spectroscopy

Vasily S. Oganesyan, Tim Rasmussen, Shirley Fairhurst, Andrew J. Thomson

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Abstract

The enzyme nitrous oxide reductase (N2OR) has a unique tetranuclear copper centre [Cu4S], called CuZ, at the catalytic site for the two-electron reduction of N2O to N2. The X- and Q-band EPR spectra have been recorded from two forms of the catalytic site of the enzyme N2OR from Paracoccus pantotrophus, namely, a form prepared anaerobically, CuZ, that undergoes a one-electron redox cycle and CuZ*, prepared aerobically, which cannot be redox cycled. The spectra of both species are axial with that of CuZ showing a rich hyperfine splitting in the g ˈ-region at X-band. DFT calculations were performed to gain insight into the electronic configuration and ground-state properties of CuZ and to calculate EPR parameters. The results for the oxidation state [Cu+13Cu+21S]3+ are in good agreement with values obtained from the fitting of experimental spectra, confirming the absolute oxidation state of CuZ. The unpaired spin density in this configuration is delocalised over four copper ions, thus, CuI 20.1%, CuII 9.5%, CuIII 4.8% and CuIV 9.2%, the µ4-sulfide ion and oxygen ligand. The three copper ions carrying the highest spin density plus the sulfide ion lie approximately in the same plane while the fourth copper ion is perpendicular to this plane and carries only 4.8% spin density. It is suggested that the atoms in this plane represent the catalytic core of CuZ, allowing electron redistribution within the plane during interaction with the substrate, N2O.

Original languageEnglish
Pages (from-to)996-1002
Number of pages7
JournalJournal of the Chemical Society. Dalton Transactions
Volume4
Issue number7
Early online date5 Mar 2004
DOIs
Publication statusPublished - 19 Mar 2004

Keywords

  • Copper
  • Density functional calculations
  • Enzymes
  • Esr spectroscopy
  • Nitrous oxide

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