Interaction of Cu(II)with His-Val-Gly-Asp and of Zn(II) with His-Val-His,Two Peptides at the Active Site of Cu,Zn-Superoxide Dismutase

His-Val-His and His-Val-Gly-Asp are two naturally occurring peptide sequences, present at the active siteof Cu,Zn-superoxide dismutase (Cu,Zn-SOD). We have already studied the interaction of His-Val-His=A(copper binding site) with Cu(II) and of His-Val-Gly-Asp=B (zinc binding site) with Zn(II). As acontinuation of this work and for comparison purposes we have also studied the interaction of Zn(II) withHis-Val-His and Cu(II) with His-Val-Gly-Asp using both potentiometric and spectroscopic methods (visible,EPR, NMR). The stoichiometry, stability constants and solution structure of the complexes formed have beendetermined. Histamine type of coordination is observed for/ZnAH/²⁺, /ZnA/⁺, /ZnA²H/⁺ and/ZnA²/ in acidic pH while deprotonation of coordinated water molecules is observed at higher pH. /CUB/ species ischaracterized by the formation of a macrochelate and histamine type coordination. Its stability results in thesuppression of amide deprotonation which occurs at high pH resulting in the formation of the highly distortedfrom square planar geometry 4N complex/CuBH_-3/³.