Stability constants of complexes of zinc and cobalt(II) ions with some histidine-containing peptides

Abstract

Equilibrium constants at 37 °C and 0·15M(KNO₃) are reported for zinc and cobalt(II) complexes of glycyl-L-histidine, glycyl-L-histidylglycine, L-histidylglycine, and carnosine from pH titration data, using a range of metal ion and ligand concentrations. Binuclear complexes are major species in solutions containing zinc ions and glycylhistidine. Related mixed complexes are formed in ternary mixtures of zinc ion, histidine, and glycylnistidine. Mixed-ligand complexes of the type MAL are also formed by zinc and cobalt(II) with histidine (HA) and the peptides. A comparison is made of the zinc-complexing abilities of the peptides in competition with α-amino-acids under physiological conditions.