A model of the copper centres of nitrous oxide reductase (Pseudomonas stutzeri)

Open Access
Publisher Website
Google Scholar
Abstract
Nitrous oxide reductase (N2OR), Pseudomonas stutzeri, catalyses the 2 electron reduction of nitrous oxide to di‐nitrogen. The enzyme has 2 identical subunits (M 1 ∼ 70 000) of known amino acid sequence and contains ∼ 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.