Copper(II)-L-glutamine complexation study in solid state and in aqueous solution

Among copper transport alterations in humans, Menkes disease is due to a lethal genetic disorder. The current treatment is the administration of physiological Cu(II)-L-histidine complex. However, this therapy is only effective in some cases and when started early in life. In order to distribute copper in all the biological compartments for Menkes disease patients, the administration of other Cu(II) amino acids complexes has been considered. Several ternary Cu(II)-amino acids complexes were detected in human serum playing an important role in the copper pathway, in particular L-histidine-Cu(II)-L-glutamine. Before the biopharmaceutical studies of L-histidine-Cu(II)-L-glutamine complex, a physicochemical characterisation of binary Cu(II)-L-glutamine complex must be conducted. Indeed, the identification of Cu(II)-L-glutamine species has not been clearly determined at physiological pH in the past. In the present work, the stoichiometry, formation constants and distribution of the various Cu(II)-L-glutamine species have been determined by polarography and UV-Vis spectroscopy in a large pH range. [Cu(II)(Gln)(2)] complex is the major component at physiological pH and its formation constant is equal to 10(12.5)I(2) mol(-2). For the first time, the structure of [Cu(II)(Gln)(2)] has been determined in the solid state and in solution. Given the small size of the obtained crystals, it has been necessary to use an X-ray synchrotron source to collect the diffraction data. X-ray crystal structure showed a 4-2 distorted octahedral geometry. In the basal plane Cu-O and Cu-N distances ranged from 1.93 to 1.98 Angstrom. Two additional oxygen atoms at 2.70 and 2.86 Angstrom complete a severely distorted octahedron. EXAFS and EPR results have shown that the structure of [Cu(II)(Gln)(2)] is preserved at physiological pH in aqueous solution. (C) 2003 Elsevier B.V. All rights reserved.