STRUCTURAL STUDIES OF THE HEMOCYANIN ACTIVE-SITE .1. EXTENDED X-RAY ABSORPTION FINE-STRUCTURE (EXAFS) ANALYSIS
STRUCTURAL STUDIES OF THE HEMOCYANIN ACTIVE-SITE .1. EXTENDED X-RAY ABSORPTION FINE-STRUCTURE (EXAFS) ANALYSIS
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血蓝蛋白活性位点的结构研究 1. 扩展 X 射线吸收精细结构（exafs）分析
DOI：
10.1021/ja00532a037
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发表时间：
1980-01-01
影响因子：
15
通讯作者：
SPIRO, TG
中科院分区：
文献类型：
--
作者：
BROWN, JM;POWERS, L;SPIRO, TG
使用同步加速器辐射获得了来自 Busycon canaliculatum 的氧合和脱氧血蓝蛋白 (Hc) 的靠近 Cu K 边缘的 X 射线吸收光谱。与 Cu 配合物的比较表明，边缘结构分别与 Cu(II) 和 Cu(I) 的咪唑配位一致。扩展精细结构 (EXAFS) 的傅里叶变换显示 2 个明确定义的峰。第一个峰的位置和形状仅需要低 Z 原子的配位，平均距离为 1.96 和 1.95 ANG。为氧-和脱氧Hc的Cu原子。计算出它们的配位数分别为4和2，但不确定性较大；根据化学和光谱证据，5 和 3 被认为是更可能的值。外部傅里叶峰将反向散射原子置于 3.7 和 3.4 ANG 处。来自氧-和脱氧Hc中的Cu。对于 oxyHc，根据重新变换的振幅函数的形状，该原子是另一个 Cu。对于脱氧 Hc，外壳峰可以与 Cu 或第一排散射体拟合。在后一种情况下，距离和所需的德拜-沃勒因子在化学上都不合理，并且 Cu-Cu 相互作用是首选解释。这些结果与共振拉曼光谱和电子吸收光谱的结果一起得出了 Hc 结合位点的模型。它有 2 个 Cu 原子，每个原子通过 3 个组氨酸配体与蛋白质结合；在 oxyHc 中，Cu(II) 离子通过结合的 O22- 和来自蛋白质配体（可能是酪氨酸）的原子桥接。
X-ray absorption spectra near the Cu K edge were obtained for oxy- and deoxyhemocyanin (Hc) from Busycon canaliculatum using synchrotron radiation. Comparison with Cu complexes shows the edge structure to be consistent with imidazole coordination of Cu(II) and Cu(I), respectively. The Fourier transform of the extended fine structure (EXAFS) shows 2 well defined peaks. The positions and shape of the 1st peaks require coordination by low-Z atoms only, at average distances of 1.96 and 1.95 .ANG. for the Cu atoms of oxy- and deoxyHc. Their coordination numbers are calculated to be 4 and 2, respectively, but the uncertainties are large; 5 and 3 are considered to be likelier values, on the basis of chemical and spectroscopic evidence. The outer Fourier peak places a backscattering atom at 3.7 and 3.4 .ANG. from Cu in oxy- and deoxyHc. For oxyHc this atom is the other Cu by the shape of the retransformed amplitude function. For deoxyHc the outer shell peak can be fit either with Cu or with a 1st-row scatterer. In the latter case neither distance nor the required Debye-Waller factor is sensible chemically, and a Cu-Cu interaction is the preferred interpretation. These results, along with those from resonance Raman and electronic absorption spectroscopy, lead to a model of the Hc binding site. It has 2 Cu atoms bound to the protein via 3 histidine ligands each; in oxyHc the Cu(II) ions are bridged by the bound O22- and by an atom from a protein ligand, possibly tyrosine.