A model of the copper centres of nitrous oxide reductase (Pseudomonas stutzeri). Evidence from optical, EPR and MCD spectroscopy.
Nitrous oxide reductase (N2OR), Pseudomonas stutzeri, catalyses the 2 electron reduction of nitrous oxide to di-nitrogen. The enzyme has 2 identical subunits (Mr approximately 70,000) of known amino acid sequence and contains approximately 4 Cu ions per subunit. By measurement of the optical absorption, electron paramagnetic resonance (EPR) and low-temperature magnetic circular dichroism (MCD) spectra of the oxidised state, a semi-reduced form and the fully reduced state of the enzyme it is shown that the enzyme contains 2 distinct copper centres of which one is assigned to an electron-transfer function, centre A, and the other to a catalytic site, centre Z. The latter is a binuclear copper centre with at least 1 cysteine ligand and cycles between oxidation levels Cu(II)/Cu(II) and Cu(II)/Cu(I) in the absence of substrate or inhibitors. The state Cu(II)/Cu(I) is enzymatically inactive. The MCD spectra provide evidence for a second form of centre Z, which may be enzymatically active, in the oxidised state of the enzyme. Centre A is structurally similar to that of CuA in bovine and bacterial cytochrome c oxidase and also contains copper ligated by cysteine. This centre may also be a binuclear copper complex.
Farrar
J A
JA
Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences, University of East Anglia, Norwich, UK.
Thomson
A J
AJ
Cheesman
M R
MR
Dooley
D M
DM
Zumft
W G
WG
D002942:Circular Dichroism; D003300:Copper / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D046911:Macromolecular Substances; D010088:Oxidoreductases / Q000737:chemistry*; D011487:Protein Conformation; D011549:Pseudomonas / Q000201:enzymology*; D013053:Spectrophotometry / Q000379:methods
D046911:Macromolecular Substances; D003300:Copper; D010088:Oxidoreductases; C022763:nitrous oxide reductase