Axial ligand modulation of the electronic structures of binuclear copper sites: analysis of paramagnetic 1H NMR spectra of Met160Gln Cu(A).

Cu(A) is an electron-transfer copper center present in heme-copper oxidases and N2O reductases. The center is a binuclear unit, with two cysteine ligands bridging the metal ions and two terminal histidine residues. A Met residue and a peptide carbonyl group are located on opposite sides of the Cu2S2 plane; these weaker ligands are fully conserved in all known Cu(A) sites.