This article reports on the extraction behavior of heme proteins from an aqueous phase into ionic liquids (ILs) with dicyclohexano-18-crown-6 (DCH18C6), and the structure−function relationship of cytochrome c (Cyt-c) dissolved in ILs. We have found that DCH18C6 enables transfer of Lys-rich proteins into ILs via supramolecular complexation. The hydrophobicity and functional groups of ILs have a great influence on protein partitioning, and a hydroxyl group-containing IL with DCH18C6 is capable of the quantitative partitioning of Cyt-c. On the other hand, protein transfer using conventional organic solvents is negligibly small. UV−visible, CD, and resonance Raman spectroscopic characterizations indicate that the sixth ligand Met 80 in the heme group of the Cyt-c−DCH18C6 complex in IL is replaced by other amino acid residues of the peptide chain and that a non-natural, six-coordinate, low-spin ferric heme structure is induced in IL. Solubilization of Cyt-c in IL causes the environmental change of the heme vicinity of Cyt-c, which triggers the functional conversion of Cyt-c from an electron-transfer protein to peroxidase. The Cyt-c−DCH18C6 complex in IL provides remarkably high peroxidase activity compared with native Cyt-c, because of enhancement of the affinity for H2O2.
本文报告了用二
环己烷-18-
冠醚-6(DCH18C6)将血红素蛋白从
水相萃取到
离子液体(ILs)中的行为,以及溶解在
离子液体中的细胞色素 c(Cyt-c)的结构-功能关系。我们发现,DCH18C6 可使富含 Lys 的蛋白质通过超分子复合物转移到 IL 中。IL的疏
水性和官能团对蛋白质的分配有很大影响,含有DCH18C6的含羟基IL能够定量分配Cyt-c。另一方面,使用传统有机溶剂的蛋白质转移量微乎其微。紫外-可见光、CD 和共振拉曼光谱表征表明,IL 中 Cyt-c-DCH18C6 复合物血红素基团中的第六
配体 Met 80 被肽链的其他
氨基酸残基取代,IL 中诱导出一种非天然、六配位、低自旋
铁血黄素结构。Cyt-c 在 IL 中的溶解会导致 Cyt-c 附近的血红素发生环境变化,从而引发 Cyt-c 从电子转移蛋白向
过氧化物酶的功能转换。与原生 Cyt-c 相比,IL 中的 Cyt-c-DCH18C6 复合物具有极高的
过氧化物酶活性,这是因为它对
H2O2 的亲和力增强了。