Protected Ac-PDEKHEL-NH2 (PK9-H) and Ac-FCGDGANDCG-NH2 (PK9-C) peptide fragments corresponding to sequences from residues 1165 to 1171 and 1184 to 1193, respectively, in the Park9 encoded protein from Parkinson's disease gene were tested for their protonation and complex formation capabilities with Cu(II), Zn(II) and Mn(II) ions by potentiometric and UV-Vis measurements. The effects of peptide titration with the metal ions have been followed by mono- and bi-dimensional NMR spectroscopy in order to support the potentiometric results and to understand the details of metal binding. Only mononuclear complexes have been evidenced for all the checked metal ions with PK9-H peptide. Mononuclear and bis-complexes with PK9-C peptide have been evidenced with Cu(II) and Zn(II) metal ions. From the dissociation-constants and pM values obtained for the binary competition diagrams for the systems containing Cu(II), Zn(II) or Mn(II) and the two ligands, the Cu(II) ion is able to bind more efficiently than Zn(II) and Mn(II) metal ions to both ligands.
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