His-Val-His and His-Val-Gly-Asp are two naturally occurring peptide sequences, present at the active site
of 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 a
continuation of this work and for comparison purposes we have also studied the interaction of Zn(II) with
His-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 been
determined. 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 is
characterized by the formation of a macrochelate and histamine type coordination. Its stability results in the
suppression of amide deprotonation which occurs at high pH resulting in the formation of the highly distorted
from square planar geometry 4N complex/CuBH-3/3.
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