cis-Urocanic acid as a potential nickel(ii) binding molecule in the human skin

cis -Urocanic acid, a derivative of histidine, is one of the essential components of human skin. We found that it can bind nickel( ii ) ions in a pH-dependent manner, with the dissociation constant in the low millimolar range, as revealed by potentiometry, and confirmed by isothermal titration calorimetry and UV-vis spectroscopy. The binding occurs within the physiological skin pH range. Considering the fact that cis -urocanic acid is present in the human skin in concentrations as high as millimolar, this molecule may be a physiologically important player in nickel trafficking in the human organism. cis -Urocanic acid, a component of human skin, is an efficient ligand for allergenic Ni 2+ ions, forming high spin complexes.