title: Chain length-dependent Pb(II)-coordination in phytochelatins.
abstract: UV/visible and circular dichroism (CD) spectroscopy have been used to study the binding of Pb(II) to plant metal-sequestering peptides, phytochelatins (PCs), with the structure (gamma Glu-Cys)2Gly, (gamma Glu-Cys)3Gly and (gamma Glu-Cys)4Gly. Saturation of the Pb(II)-induced charge-transfer bands indicated that both (gamma Glu-Cys)2Gly and (gamma Glu-Cys)3Gly bound one metal ion per peptide molecule. However, (gamma Glu-Cys)4Gly formed two distinct species with stoichiometries of one and two Pb(II) ions per peptide molecule, respectively. The optical spectra of Pb(II)1-(gamma Glu-Cys)4Gly were similar to those of Pb(II)1-(gamma Glu-Cys)3Gly, whereas the spectra of Pb(II)2-(gamma Glu-Cys)4Gly were similar to those of Pb(II)1-(gamma Glu-Cys)2Gly. Since cysteinyl thiolates are the likely ligands for Pb(II) in PCs, Pb(II) appears to form two-, three- and four-coordinate complexes with PCs depending on their chain length. Furthermore, Pb(II) may exhibit multiple coordination in longer chain PCs as indicated by the formation of two Pb(II)-binding species of (gamma Glu-Cys)4Gly. The transfer of Pb(II) from glutathione to PCs and from shorter chain to longer chain PCs is also demonstrated.
mesh_terms: D000818:Animals; D002413:Cations, Divalent; D002942:Circular Dichroism; D005978:Glutathione; D007854:Lead / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008667:Metalloproteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D008668:Metallothionein / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D054811:Phytochelatins; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D013053:Spectrophotometry / Q000379:methods
chemical_list: D002413:Cations, Divalent; D008667:Metalloproteins; D010940:Plant Proteins; D007854:Lead; D008668:Metallothionein; D054811:Phytochelatins; D005978:Glutathione