The interaction of Zn2+ with angiotensin I, a decapeptide containing two histidyl residues, has been studied by 1H-NMR spectroscopy in both water and dimethylsulfoxide. When Zn2+ is added to the peptide in dimethylsulfoxide, binding occurs by coordination of the imidazole rings of both histidines to the metal-ion, enabling the deprotonation of the Phe peptide nitrogen.
