Spectroscopy, coupled with EXAFS , and fast reaction kinetic studies such as pulse radiolysis, have been used extensively to help understand the structure and active sites in the copper proteins.
See azurin example: 184K pdf
Cu(II) has a d9-electron configuration, copper also has two isotopes, Cu63 and Cu65, both with nuclear spin I = 3/2, and differing only slightly in their magnetic moments. The single unpaired electron and the nuclear spin give rise to EPR spectra with g-values and hyperfine splitting parameters which are very characteristic of the surrounding ligand geometry and type. Thus Electron Magnetic Resonance techniques have frequently been used to examine the blue copper enzymes. It is also important to understand that this spectrum only gives a picture of the Cu(II) ions, the Cu(I) (a d10 ion) is EPR silent.