The essential Cu(I) and the toxic Hg(II) ions possess similar coordination properties, and therefore, similar cysteine rich proteins participate in the control of their intracellular concentration. In this work we present the metal binding properties of linear and cyclic model peptides incorporating the three-cysteine motifs, CxCxxC or CxCxC, found in metallothioneins. Cu(I) binding to the series of peptides at physiological pH revealed to be rather complicated, with the formation of mixtures of polymetallic species. In contrast, the Hg(II) complexes display well-defined structures with spectroscopic features characteristic for a HgS₂ and HgS₃ coordination mode at pH = 2.0 and 7.4, respectively. Stability data reflect a ca. 20 orders of magnitude larger affinity of the peptides for Hg(II) (log β^pH7.4_HgP ≈ 41) than for Cu(I) (log β^pH7.4_CuP ≈ 18). The different behaviour with the two metal ions demonstrates that the use of Hg(II) as a probe for Cu(I), coordinated by thiolate ligands in water, may not always be fully appropriate.

中文翻译：

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具有三个半胱氨酸残基的短寡肽作为蛋白质中富含硫的Cu（i）和Hg（ii）结合位点的模型†

必需的Cu（I）和有毒的Hg（II）离子具有相似的配位特性，因此，相似的富含半胱氨酸的蛋白质参与了其细胞内浓度的控制。在这项工作中，我们介绍了结合了金属硫蛋白中的三个半胱氨酸基序CxCxxC或CxCxC的线性和环状模型肽的金属结合特性。在生理pH下，Cu（I）与一系列肽的结合被揭示是相当复杂的，形成了多金属物种的混合物。相比之下，Hg（II）配合物显示出结构明确的结构，具有HgS ₂和HgS _3的光谱特征pH = 2.0和7.4时的配位模式。稳定性数据反映出约 对Hg（肽的大小较大的亲和力的20项目II）（对数 β ^pH7.4的_HGP ≈41）比的Cu（我）（日志 β ^pH7.4的_杯≈18）。两种金属离子的不同行为表明，使用Hg（II）作为Cu（I）的探针（由水中的硫醇盐配体配位）可能并不总是完全合适的。