Transition metal ion binding studies of carnosine and histidine: biologically relevant antioxidants.

Carnosine and histidine are biologically interesting antioxidants. In order to probe whether they exert their antioxidant effect through metal ion chelation, the Cu(II) ion chelating abilities of these compounds were measured by UV-vis spectroscopy. Both of these compounds showed 1:1 complexations with Cu(II) ions as shown by their Job's plot. The binding constants for histidine and carnosine, as determined by Benesi-Hildebrand method, at pH 7.84+/-0.18, were found to be 71 and 1.1M(-1), respectively. The unexpectedly lower binding constant values of carnosine show the relatively minor role of the transition metal ion chelation in their antioxidant abilities.