Towards accurate structural characterization of metal centres in protein crystals: the structures of Ni and Cu T₆ bovine insulin derivatives

The level of structural detail around the metal sites in Ni²⁺ and Cu²⁺ T₆ insulin derivatives was significantly improved by using a combination of single-crystal X-ray crystallography and X-ray absorption spectroscopy. Photoreduction and subsequent radiation damage of the Cu²⁺ sites in Cu insulin was followed by XANES spectroscopy.