Interaction of Cu2+ with His-Val-His and of Zn2+ with His-Val-Gly-Asp, twopeptides surrounding metal ions in Cu,Zn-superoxide dismutase enzyme

His-Val-His and His-Val-Gly-Asp are two naturally occuring peptide sequence s, present at the active site of Cu,Zn-superoxide dismutase (Cu,Zn-SOD). Th e interactions of His-Val-His=A (copper binding site) with Cu(II) and of Hi s-Val-Gly-Asp=B (zinc binding site) with Zn(II) have been studied by using both potentiometric and spectroscopic methods (visible, EPR, NMR). The stoi chiometry, stability constants and solution structure of the complexes form ed have been determined. The binding modes of the species [CuAH](2+) and [C uA](+) were characterized by histamine type of coordination. [CuA](+) is fu rther stabilized by the formation of a macrochelate with the involvement of the imidazole of the C-terminal histidine. The existence of macrochelate r esults in a slight distortion of the coordination geometry providing good b ase for the development of enzyme models. The enhanced stability of the mac rochelate suppresses the formation of bis-complexes as well as the amide de protonation. This process, however, takes place at higher pH resulting in t he formation of the 4 N- coordinated [NH2,N-,N-,N(im)] species [CuAH(2-)](- ). On the other hand, in the case of the Zn(Il)-His-Val-Gly-Asp system, coo rdination takes place at the terminal carboxylate in species [ZnBH2](2+). M onodentate binding occurs via the N-terminal imidazole in [ZnBH](+) while h istamine type of coordination is possible in [ZnB], [ZnB2H](-) and [ZnB2](2 -) species. Amide deprotonation does not take place in the case of Zn2+, hy droxo-complexes are formed instead. (C) 2001 Elsevier Science B.V. All righ ts reserved.