Equilibrium and detailed spectroscopic characterization of zinc(II) complexes with NiSOD binding loop and their related model fragments are reported in the whole investigated pH-range. The zinc(II) complexes of L1 (HCDLPCGVY-NH₂), L2 (Ac-HCDLPCGVY-NH₂) and L3 (HCDLACGVY-NH₂) and the nickel(II) and zinc(II) complexes of L4 (HCDLPCG-NH₂) were studied by pH-potentiometric and several spectroscopic methods. The results indicated that the macrochelate coordinated zinc(II) complexes are dominant in a whole pH-range and the side chain donors of the peptides are involved in the metal binding. Therefore, the deprotonation and coordination of the peptide backbone occur only in a strongly alkaline solution. The acetylation of the peptide amino terminus (L2) significantly enhances the zinc(II) binding ability compared to the corresponding nickel(II) complexes. L2 complexes of zinc(II) are 2 or 3 orders of magnitude more stable than the corresponding nickel(II) complexes. This effect clearly shows the crucial role of the terminal amino group in the nickel binding for the NiSOD enzyme.