"Classical" Copper Centers in Proteins

Copper participates in many biological processes involving electron transfer reactions. Its roles are as widely varied as simple electron transfer, oxygen activation, and oxygen transport.


In this sense, the copper proteins often have functions which can be carried out by iron centers. This is an indication that natural evolution was "success-oriented" and not "structure-oriented." A good example of this is the enzyme nitrite reductase. Its active site can be either an iron haem center or a type I copper complex.


Copper proteins are often classified as type I, type II, or type III centers, depending on the environment of the metal ion and spectroscopic characteristics (EPR spectrum, color, etc).

Type I ("blue" copper proteins)

Type II ("non-blue" copper proteins)


Type III (dimers)



  • Strongly distorted coordination sphere (3 + 1) comprised of 2x histidine, 1x methionine, 1x cysteine
  • Absorption at ca. 600 nm (blue)
  • EPR spectrum with small Cu coupling and g-value anisotropy:
  • Essentially planar coordination sphere with 3x histidine und 1x H2O or substrate molecule
  • Weak absorption in the visible region
  • EPR spectrum with axial symmetry ("normal" EPR spectrum):
  • Oxygen bridged dimer with a Cu-Cu distance of ca. 360 pm
  • After oxygen uptake shows intense absorptions at 350 nm and 600 nm
  • EPR silent; antiferromagnetically coupled d9 centers:
Examples: plastocyanin, azurin,
                 nitrite reductase
Examples: galactose oxidase, amine oxidase,
                 dopamine monooxidase
Examples: haemocyanin, tyrosinase