Binuclear Copper A : Part 6. Copper ; Binuclear Copper : CuA Copper

Abstract

The purple CuA is a Cys-bridged, mixed-valence electron transfer center [Cu(1.5+)…Cu(1.5+)], found in cytochrome c oxidase and in nitrous oxide reductase. More recently, the NO reductase from Bacillus azotoformans was identified as the third CuA-containing enzyme. There also exist engineered CuA sites which have been introduced by loop-directed mutagenesis into blue type 1 copper proteins, such as azurin or amicyanin. Electron transfer mediated by CuA is very efficient. The reasons for utilizing a binuclear electron transfer center in cytochrome c oxidase and nitrous oxide reductase, instead of mononuclear type 1 Cu, are suggested to be its unidirectional electron transfer through the site or the lower energy of reorganization. Interest in CuA is directly related to its unique spectroscopic properties. Studies by paramagnetic resonance, magnetic circular dichroism, resonance Raman, and X-ray absorption spectroscopy have provided a clear picture of the electronic properties of the CuA site and the interaction of the metal atoms with the neighboring amino acids.