CHELATION CHEMISTRY OF CARNOSINE - EVIDENCE THAT MIXED COMPLEXES MAY OCCUR INVIVO

The ability of L-carnosine to chelate various metal ions in both the presence and absence of competing ligands was tested with 1H NMR, ESR, and UV-visible absorption spectroscopies. Zinc(II) and cadmium(II) ions were observed to produce weak complexes with carnosine, anserine, and homocarnosine without changing the conformation of the dipeptide. These complexes do not appear to be affected by addition of histidine or cysteine. Copper(II) ion forms three structurally different complexes with carnosine at physiological pH and temperature depending on the relative concentrations of copper(II) ion and carnosine. One of these complexes has a magnetically coupled cupric dimer, and the others have a monomeric copper(II) ion. When either histidine, cysteine or glutathione is added to a solution of copper(II)-carnosine, a complex with a monomeric copper(II) ion is favored by formation of a mixed complex that contains both ligands. The possible significance of the various complexes of carnosine and its analogues with metal ions including zinc, cadmium, and copper(II) with regard to the metabolism of these metals in vivo is discussed. © 1979 American Chemical Society.