Department of Chemistry, Presidency University, Kolkata 700 073, India.
Department of Chemistry, Presidency University, Kolkata 700 073, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2018 Jun 5;198:278-282. doi: 10.1016/j.saa.2018.03.026. Epub 2018 Mar 12.
The interactions of a protein cytochrome c with some selected conventional and ionic liquid surfactants have been investigated at pH7.4 using ultraviolet-visible and fluorescence spectroscopic techniques. We used four conventional surfactants - cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), sodium N-dodecanoylsarcosinate (SDDS), and N-decanoyl-N-methylglucamine (Mega 10), and a surface active ionic liquid 1-hexadecyl-3-methylimidazolium chloride (CMeImCl). All the investigated surfactants were found to induce an unfolding of the protein cytochrome c. In presence of CTAB, SDDS and CMeImCl, the heme iron atom was found to loose methionine from its axial position. Differential binding of the surfactant monomers and their micelles to the protein molecules was inferred. The ionic surfactants were found to be more effective than the nonionic one in unfolding the investigated protein. However, the extent of binding of CTAB/CMeImCl to cytochrome c reaches a plateau past the critical micellization concentration (cmc) of the surfactant. For each of the cytochrome c-DTAB, cytochrome c-SDDS and cytochrome c-Mega 10 system, although there exists an inflection in the surfactant-binding, saturation point could not be detected. It has been demonstrated from the ultraviolet-visible spectral studies that the oxidation state of iron in cytochrome c does not change when the protein binds with the investigated surfactants.
使用紫外可见光谱和荧光光谱技术研究了在 pH7.4 下蛋白质细胞色素 c 与一些选定的常规和离子液体表面活性剂的相互作用。我们使用了四种常规表面活性剂 - 十六烷基三甲基溴化铵（CTAB）、十二烷基三甲基溴化铵（DTAB）、N-十二酰基肌氨酸钠（SDDS）和 N-癸酰基-N-甲基葡糖胺（Mega 10），以及一种表面活性离子液体 1-十六烷基-3-甲基咪唑氯化物（CMeImCl）。所有研究的表面活性剂都被发现诱导蛋白质细胞色素 c 的展开。在 CTAB、SDDS 和 CMeImCl 存在下，血红素铁原子被发现从其轴向位置失去蛋氨酸。推断出表面活性剂单体及其胶束与蛋白质分子的差分结合。离子表面活性剂被发现比非离子表面活性剂更有效地展开所研究的蛋白质。然而，CTAB/CMeImCl 与细胞色素 c 的结合程度在表面活性剂的临界胶束浓度（cmc）之后达到平台。对于每个细胞色素 c-DTAB、细胞色素 c-SDDS 和细胞色素 c-Mega 10 体系，尽管存在表面活性剂结合的拐点，但未检测到饱和点。从紫外可见光谱研究表明，当蛋白质与研究的表面活性剂结合时，细胞色素 c 中的铁的氧化态不会改变。
