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首页> 外文期刊>Biochemistry >Plastocyanin binding to photosystem I as a function of the charge state of the metal ion: effect of metal site conformation.
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Plastocyanin binding to photosystem I as a function of the charge state of the metal ion: effect of metal site conformation.

机译：视花青素与光系统I的结合随金属离子电荷状态的变化而变化：金属位点构象的影响。

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The binding of Ag- and Cd-substituted plastocyanin to reduced photosystem 1 of spinach has been studied through the rotational correlation time of plastocyanin measured by the technique of perturbed angular correlation of gamma-rays (PAC). Ag and Cd are used as models for native Cu(I) and Cu(II), respectively. A dissociation constant of 5 microM was found for Ag-plastocyanin, whereas the dissociation constant was at least 24 times higher for Cd-plastocyanin. PAC was further used to characterize the structure of the metal site of Cd- and Ag-plastocyanin. The Cd spectra are characteristic of a planar configuration of one cysteine and two histidines. However, the spectra show an unusual peak broadening and a high degree of internal motion, interpreted as motion of one of the histidines within the plane. (111)Ag decays to (111)Cd, followed by the emission of two gamma-rays used for the PAC experiment. The (111)Ag PAC spectra indicate that one of the coordinating histidines has a different position in the Ag protein than in the Cd protein but that the decay of Ag to Cd causes a relaxation of the position of this histidine to the position in the Cd protein within 20 ns. Binding of Ag-plastocyanin to photosystem I stabilized the Ag metal site structure so that no relaxation was observed on a time scale of 100 ns. This stabilization of the Ag structure upon binding indicates that the metal site structure is involved in regulating how the dissociation constant for plastocyanin depends on the charge of the metal ion.
机译：通过利用γ射线（PAC）的扰动角相关技术测量的质体蓝素的旋转相关时间，研究了Ag和Cd取代的质体蓝素与菠菜还原光系统1的结合。 Ag和Cd分别用作天然Cu（I）和Cu（II）的模型。 Ag-质体蓝蛋白的解离常数为5 microM，而Cd-质体蓝蛋白的解离常数至少高24倍。 PAC还用于表征Cd和Ag质体蓝蛋白的金属位点结构。 Cd光谱是一个半胱氨酸和两个组氨酸的平面构型的特征。然而，光谱显示出异常的峰展宽和高度的内部运动，这被解释为平面中组氨酸之一的运动。 （111）Ag衰减至（111）Cd，然后发射用于PAC实验的两条伽马射线。 （111）Ag PAC光谱表明，其中一个配位组氨酸在Ag蛋白中的位置与在Cd蛋白中的位置不同，但是Ag降解为Cd导致该组氨酸的位置松弛到Cd中的位置20 ns内的蛋白质。 Ag-质体蓝蛋白与光系统I的结合稳定了Ag金属位点结构，因此在100 ns的时间范围内未观察到松弛。结合后Ag结构的这种稳定化表明金属位点结构参与调节质体蓝素的解离常数如何取决于金属离子的电荷。

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