Structural studies of the hemocyanin active site. 2. Resonance Raman spectroscopy
Structural studies of the hemocyanin active site. 2. Resonance Raman spectroscopy
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血蓝蛋白活性位点的结构研究。
DOI：
10.1021/ja00532a038
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发表时间：
1980
影响因子：
15
通讯作者：
T. Spiro
中科院分区：
文献类型：
--
作者：
J. Larrabee;T. Spiro
pxyhemocyanin的拉曼光谱显示，在350 cm-1以下的模式有很强的增强，其中一些模式可以通过63Cu/65Cu和H2O/D2O的频移来分配给铜-咪唑的拉伸振动。节肢动物和软体动物的蛋白质表现出不同的强度模式，尽管同一类中不同物种的蛋白质表现出相同的模式。同位素位移表明咪唑锂基团的不对称分布，频率与两个咪唑共用一个四方平面，配体桥接两个Cu2+离子，第三个咪唑占据顶端位置一致。0-0拉伸模式的增强要低得多，与在570 nm吸收波段共振时观察到的增强相当，尽管后者的吸收率低20倍。与这两个跃迁相关的frank - condon产物的隐含差异与它们分配给两个不同的022-*轨道的电荷转移跃迁是一致的。高能量跃迁与低能量轨道有关，相对于0-0键，低能量轨道的反键性较小。令人惊讶的是，Cu-02拉伸模式没有被检测到；其强度必须至少比0-0拉伸低五倍。在1075 cm-1处可以看到宽（~ 50 cm-1）的拉曼带，这是由于电子拉曼效应。提出了Cu2+对的单重态-三重态跃迁。
Raman spectra of pxyhemocyanin, excitedin resonance with theintense 345-nm absorption, show strong enhance-ment of modes below 350 cm-1, some of which are assignable to copper-imidazole stretching vibrations via 63Cu/65Cu and H2O/D2O frequency shifts. Arthropod and mollusc proteins show somewhat different intensity patterns, although different species within the same class show the same pattern. The isotope shifts imply an asymmetric disposition of the imidazole li-gands, and the frequencies are consistent with two imidazoles sharing a tetragonal plane with the ligands bridging the two Cu2+ ions, and a third imidazoleoccupying an apical position. Enhancement of the 0-0 stretching mode is much lower, and is comparable to that observed for resonance with the 570-nm absorptionband, despite the 20-fold lower absorptivity of the latter. The implied disparity in the Franck-Condon productsassociated with thetwo transitions is consistent with their assignment to charge-transfer transitionsfrom the two different 022-* orbitals. The higherenergy transition is associated with the lower energy orbital, which is less antibonding with respect to the 0-0 bond. Surprisingly, the Cu-02 stretching mode has not been detected; its intensity must be at least fivefold lower than that of the 0-0 stretch. A broad (~ 50 cm-1) Raman band is seen at 1075 cm-1, which is attributable to an electronic Raman effect. Assignment to thesinglet-» triplet transition of the coupled Cu2+ pair is suggested.