Specific Metal Ion Recognition Mechanism by Protein Molecule

伪azurin的紫外共振拉曼光谱在1385 cm^<-1>处形成铜配位组氨酸咪唑带。在酸性pH下，Cu(I) pseudoazurin的UVRR光谱中检测到1408 cm^<-1>的组氨酸咪唑拉曼特征带。这支持了在低pH值下还原蛋白中His81配体的质子化。在中性pH下，以Zn^<2+>取代的咪唑类伪azurin在1388 cm^<-1>处呈现出特征拉曼带。随着pH的降低，Zn^<2+>类伪azurin中的组氨酸咪唑带强度减弱。在所有金属取代的伪azurin中，pH < 4.0时出现了1408 cm^<-1>的咪唑带。用Zn^<2+>、Cd^<2+>和Ni^<2+>取代的伪azurin，其X-Pro拉曼谱带的pH依赖性与载伪azurin非常相似。这些结果表明，在酸性pH下，金属离子从Zn^<2+>, Cd^<2+>和Ni^<2+>的活性位点释放，并伴随着蛋白质二级结构的改变。这种行为在Cu(I)和Cu（II）蛋白中明显不存在，这表明伪azurin可以区分铜和所研究的其他金属离子。

The UV resonance Raman spectrum of pseudoazurin gives a copper coordinated histidine imidazole band at 1385 cm^<-1>. A characteristic histidine imidazolium Raman band at 1408 cm^<-1> is detected in the UVRR spectrum of Cu(I) pseudoazurin at acidic pH. This supports the protonation of the His81 ligand in the reduced protein at low pH values. The imidazolium Pseudoazurin substituted with Zn^<2+> gave characteristic Raman Bands for the metal ion coordinated imidazole at 1388 cm^<-1> at neutral pH. The histidine imidazole band diminishes in intensity in Zn^<2+> pseudoazurin upon lowering the pH. In all of the metal-substituted pseudoazurins an imidazolium band at 1408 cm^<-1> appears at pH < 4.0. Pseudoazurin substituted with Zn^<2+>, Cd^<2+>, and Ni^<2+> give very similar pH dependence of their X-Pro Raman bands as apo-pseudoazurin. These findings indicate that the metal ion is released from the active site of Zn^<2+>, Cd^<2+>, and Ni^<2+> pseudoazurin at acidic pH accompanied by a change in the protein's secondary structure. This behavior is clearly absent in both the Cu(I) and CU(II) proteins indicating that pseudoazurin discriminates between copper and the other metal ions studied.