Stopped-Flow Spectroscopic Studies on the Ligand-Exchange Reaction of Cu–(Glycine-Peptide) Complexes, Cu(H<sub>−<i>i</i></sub>L), with Cysteine. Cu(II) Transport and Characterization of the Intermediate Ternary Complexes Cu(H<sub>−1</sub>L)(Cys<sup>−</sup>); L = Glycylglycine (<i>i</i>= 1), Triglycine (<i>i</i>= 2), Tetraglycine (<i>i</i>= 2 or 3), and Pentaglycine (<i>i</i>= 2 or 3)
作者:Akira Hanaki、Manabu Hiraoka、Toshikazu Abe、Yasuhiro Funahashi、Akira Odani
DOI:10.1246/bcsj.76.1747
日期:2003.9
Cu(II) complexes of glycine-peptides, abbreviated as Cu(H−iL): L = glycylglycine, triglycine, tetraglycine, and pentaglycine (i = 1–3), react with cysteine to form ternary complexes, Cu(H−1L)(Cys−), as first intermediates. The spectral parameters of the ternary complexes, which were similar irrespective of the peptides, were as follows: λmax = 332 ± 1 nm (ε = 4250 ± 50 M−1 cm−1), g|| = 2.170 ± 0.005, g⊥ = 2.00 ± 0.05, and A|| = (2.05 ± 0.01) × 10−4 cm−1, indicating that the ternary complexes have identical coordination structures: the Cu(II) coordinates with the peptides via the nitrogens from the terminal amino and the neighboring deprotonated-amide group, and with cysteine via the amino nitrogen and the thiolate sulfur. Based on the absorbance-time curves, the concentrations of each Cu(II) and Cu(I) species during the reaction were calculated. The species distribution curve clearly visualized the pathway of the Cu(II) transport from Cu(H−iL) to Cu(Cys−)2 via Cu(H−1L)(Cys−). The rate of Cu(H−1L)(Cys−) formation, which was evaluated from the initial increase in the species distribution curve, depended on the coordination modes of the Cu(H−iL) complexes. Both the Cu(H−1L), involving N,N−,O−,O* donors, and the Cu(H−2L), involving N,N−,N−,O−* donors, rapidly formed Cu(H−1L)(Cys−) complexes, where the donors asterisked represent the fourth ligand in the Cu(H−iL) complexes. The second-order rate constant, k1+, was on the order of 106 M−1 s−1, or bigger. The Cu(H−3L), involving N,N−,N−,N−* donors, reacted relatively slowly; k1+ was on the order of 104 M−1 s−1. Those results indicate that the affinity of the Cu(II) for the fourth donor in Cu(H−iL) determines the rate of metal-transport.
甘氨酸肽的Cu(II)配合物,简称Cu(H−iL):L =甘氨酰甘氨酸、三甘氨酸、四甘氨酸和五甘氨酸(i = 1–3),与半胱氨酸反应形成三元配合物Cu(H−1L)(Cys−),作为最初中间体。这些三元配合物的光谱参数相似,无论肽的种类如何,其参数如下:λmax = 332 ± 1 nm (ε = 4250 ± 50 M−1 cm−1), g|| = 2.170 ± 0.005, g⊥ = 2.00 ± 0.05, 和 A|| = (2.05 ± 0.01) × 10−4 cm−1,表明三元配合物具有相同的配位结构:Cu(II)通过来自末端氨基和相邻的去质子化酰胺基团的氮原子与肽配位,并通过氨基氮和硫醇盐硫与半胱氨酸配位。根据吸光度-时间曲线,计算了反应过程中每种Cu(II)和Cu(I)物种的浓度。物种分布曲线清楚地显示了Cu(II)从Cu(H−iL)经Cu(H−1L)(Cys−)到Cu(Cys−)2的传递途径。Cu(H−1L)(Cys−)形成的速率,从物种分布曲线的初始增加中评估,取决于Cu(H−iL)配合物的配位模式。涉及N,N−,O−,O*供体的Cu(H−1L)和涉及N,N−,N−,O−*供体的Cu(H−2L)迅速形成Cu(H−1L)(Cys−)配合物,其中带星号的供体表示Cu(H−iL)配合物中的第四个配体。二阶速率常数k1+在106 M−1 s−1的量级,或更大。涉及N,N−,N−,N−*供体的Cu(H−3L)反应相对较慢;k1+在104 M−1 s−1的量级。这些结果表明,Cu(II)对Cu(H−iL)中第四个供体的亲和力决定了金属传递的速率。