Studies of cation binding in ZnCl2-regenerated bacteriorhodopsin by x-ray absorption fine structures: effects of removing water molecules and adding Cl- ions.
Studies of cation binding in ZnCl2-regenerated bacteriorhodopsin by x-ray absorption fine structures: effects of removing water molecules and adding Cl- ions.
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通过 X 射线吸收精细结构研究 ZnCl2 再生细菌视紫红质中的阳离子结合：去除水分子和添加 Cl- 离子的影响。
DOI：
10.1016/s0006-3495(97)78240-7
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发表时间：
1997
影响因子：
3.4
通讯作者：
El-Sayed,MA
中科院分区：
文献类型：
--
作者：
Zhang,K;Song,L;Dong,J;El-Sayed,MA
用X射线吸收精细结构（XAFS）研究了不同条件下Zn ~（2+）-再生细菌视紫红质（bR）中Zn ~（2+）的结合。0.9：1和2：1的Zn ~（2+）：bR样品的XAFS光谱相似，表明Zn ~（2+）在bR中可能只有一个强结合位点。结果表明，在bR水溶液中，Zn ~（2+）平均有6个氧或氮配体。在干燥时，两个配体丢失，这表明在细菌视紫红质的阳离子结合位点附近存在两个弱结合的水配体。当过量的Cl-离子存在于干燥之前的Zn 2+再生的bR样品中，它被发现，两个配体被取代的Cl-离子在干燥的膜，而两个保持不变。以上观察表明，Zn 2+在再生bR中具有三种类型的配体（称为I、II和III型）。I型配体是强结合的。这些配体不能通过干燥或与Cl-离子交换来去除。II型配体不能通过干燥除去，但可以被Cl-配体取代。III型配体与金属阳离子弱结合，并且最有可能是水分子，其可以通过在真空下蒸发或通过用无水CaSO 4干燥来去除。对bR中Zn ~（2+）强结合位点的可能结构进行了讨论。
The binding of Zn2+ in Zn2+-regenerated bacteriorhodopsin (bR) was studied under various conditions by x-ray absorption fine structures (XAFS). The 0.9:1 and 2:1 Zn2+:bR samples gave similar XAFS spectra, suggesting that Zn2+ might have only one strong binding site in bR. It was found that in aqueous bR solution, Zn2+ has an average of six oxygen or nitrogen ligands. Upon drying, two ligands are lost, suggesting the existence of two weakly bound water ligands near the cation-binding site in bacteriorhodopsin. When excess Cl- ions were present before drying in the Zn2+-regenerated bR samples, it was found that two of the ligands were replaced by Cl- ions in the dried film, whereas two remain unchanged. The above observations suggest that Zn2+ has three types of ligands in regenerated bR (referred to as types I, II, and III). Type I ligands are strongly bound. These ligands cannot be removed by drying or by exchanging with Cl- ions. Type II ligands cannot be removed by drying, but can be replaced by Cl- ligands. Type III ligands are weakly bound to the metal cation and are most likely water molecules that can be removed by evaporation under vacuum or by drying with anhydrous CaSO4. The results are discussed in terms of the possible structure of the strongly binding site of Zn2+ in bR.