Mehra R K, Kodati V R, Abdullah R
Department of Entomology, University of California, Riverside 92521, USA.
Biochem Biophys Res Commun. 1995 Oct 13;215(2):730-6. doi: 10.1006/bbrc.1995.2524.
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.
紫外/可见光谱和圆二色光谱（CD）已被用于研究铅（II）与植物金属螯合肽——植物螯合素（PCs）的结合，植物螯合素的结构为（γ-谷氨酰-半胱氨酸）2甘氨酸、（γ-谷氨酰-半胱氨酸）3甘氨酸和（γ-谷氨酰-半胱氨酸）4甘氨酸。铅（II）诱导的电荷转移带的饱和表明，（γ-谷氨酰-半胱氨酸）2甘氨酸和（γ-谷氨酰-半胱氨酸）3甘氨酸每个肽分子都结合一个金属离子。然而，（γ-谷氨酰-半胱氨酸）4甘氨酸形成了两种不同的物种，每个肽分子分别具有一个和两个铅（II）离子的化学计量比。Pb（II）1-（γ-谷氨酰-半胱氨酸）4甘氨酸的光谱与Pb（II）1-（γ-谷氨酰-半胱氨酸）3甘氨酸的光谱相似，而Pb（II）2-（γ-谷氨酰-半胱氨酸）4甘氨酸的光谱与Pb（II）1-（γ-谷氨酰-半胱氨酸）2甘氨酸的光谱相似。由于巯基半胱氨酸盐可能是植物螯合素中铅（II）的配体，铅（II）似乎根据植物螯合素的链长与它们形成二配位、三配位和四配位的配合物。此外，如（γ-谷氨酰-半胱氨酸）4甘氨酸形成两种铅（II）结合物种所示，铅（II）在较长链的植物螯合素中可能表现出多重配位。还证明了铅（II）从谷胱甘肽向植物螯合素以及从较短链植物螯合素向较长链植物螯合素的转移。
