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, CXnC (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)
The systematic study of small cysteine containing peptides reveals the outstanding Pb(II)‐ and Cd(II)‐binding ability of peptides with CXnC (n=0–3) sequence. This is well demonstrated by pM values calculated for different metal‐peptide systems at pH 7 (cL=0.010 mM, cM=0.001 mM).