Metal Binding Ability of Small Peptides Containing Cysteine Residues

The Cd(II)-, Pb(II)-, Ni(II)- and Zn(II)-complexes of small terminally protected peptides containing CXXX, XXXC, XCCX, CX_nC (n=1–3) sequences have been studied with potentiometric, UV/Vis and CD spectroscopic techniques. The cysteine thiolate group is the primary binding site for all studied metal ions, but the presence of a histidyl or aspartyl side chain in the molecule contributes to the stability of the complexes. For two-cysteine containing peptides the (S⁻,S⁻) coordinated species are formed in the physiological pH range and the stability increases in the Ni(II)