Electronic structures of blue copper centers of amicyanin and azurin in the solution state

Abstract

X-ray absorption near edge structure (XANES) spectra of blue copper proteins, amicyanin and azurin, in the solution state were measured in the copper L₃-edge energy region. The absorption peak energies were quite similar for both proteins, while the main edge region for azurin was broader than that for amicyanin, owing to more pronounced shoulder spectral features in the former. Ab initio calculations at the whole protein level qualitatively reproduced the experimental spectra well. The relative X-ray absorption intensities suggest that the degree of covalency of the copper–ligand bond at the active site was weaker for amicyanin than that for azurin.