不同类型表面活性剂与高铁肌红蛋白相互作用

Interactions between Different Classes of Surfactants and Metmyoglobin

通过UV-Vis吸收光谱、同步荧光光谱、圆二色(CD)光谱等方法对阴离子型表面活性剂——琥珀酸二辛酯磺酸钠(AOT)和十二烷基苯磺酸钠(SDBS)、阳离子型表面活性剂——十六烷基三甲基溴化铵(CTAB)和十二烷基三甲基溴化铵(DTAB)、两性离子型表面活性剂——3-[(3-胆固醇氨丙基)二甲基氨基]-1-丙磺酸(CHAPS)与马心高铁肌红蛋白(metMb)的不同作用机理进行了探讨.结果显示:阴、阳离子型表面活性剂可以与蛋白发生较强烈的作用,且相互作用与表面活性剂的浓度密切相关.AOT和SDBS浓度的升高使得metMb的Soret带发生红移且出现两个新的Q带,伴随着配体金属电荷转移(LMCT)带的消失,蛋白从水合的六配位高自旋复合物(6-cHs)转化成六配位低自旋高铁血红素复合物(6-cLs),低浓度的AOT和SDBS对Tyr和Trp微环境均有影响,能使metMb的二级结构发生变化;而CTAB和DTAB在低浓度时对metMb的血红素中心影响不大,但是对Trp和Tyr的微环境影响很大,高浓度时主要通过静电吸引作用以聚合体形式直接作用于血红素中心,使Soret带发生蓝移,metMb形成五配位高自旋(5-cHs)复合物,血红素从疏水腔中释放出来,metMb的α螺旋含量减少.DTAB由于自身结构的特点,与CTAB作用于蛋白的过程有些区别,形成了一个中间态,但最终也导致血红素的暴露.两性离子型表面活性剂在测定浓度范围内不与metMb发生作用,原因是CHAPS整体呈电中性,其与metMb的阴离子性或者阳离子性位点作用的能力很弱,同时也说明metMb表面带相反电荷的位点相距较远.结果充分证明表面活性剂与蛋白相互作用的方式与表面活性剂的种类、结构及其浓度有关.

Abstract： Complexes of horse metmyoglobin （metMb） with the anionic surfactants sodium bis（2- ethylhexyl） sulfosuccinate （AOT） and sodium dodecyl benzene sulfonate （SDBS）, the cationic surfactants dodecyl trimethylammonium bromide （CTAB） and dodecyltrimethyl ammonium bromide （DTAB）, and the zwitterionic surfactant 3-[（3-cholamidopropyl） dimethylammonio] propanesulfonate （CHAPS） were investigated by UV-Vis absorption, synchronous fluorescence emission, and circular dichroism （CD） spectroscopy. Experimental results show that the anionic and cationic surfactants can interact with metMb intensively depending on the surfactant concentration. The UV-Vis spectra indicate that AOT and SDBS interact with metMb at low concentrations. The addition of AOT （or SDBS） causes the formation of a six-coordinated low-spin heme （6-cLs） hemichrome as is evident from the red shift of the Soret band, the intensity decrease, concomitant appearance of two new Q bands, and the disappearance of ligand- to-metal charge transfer （LMCT）. The surfactants disturb the Tyr and Trp microenvironment and change the second structure parameter of metMb while the e-helix content decreases. However, the interaction between metMb and CTAB （or DTAB） is different. They cannot disturb heme at very low concentrations but can disturb the Tyr and Trp microenvironment. CTAB and DTAB aggregates can convert metMb to a five-coordinated low-spin heme as shown by the blue shift of the Soret band and cause the heme monomer to leave the hydrophobic cavity of metMb through electrostatic attraction mainly. DTAB/metMb complexes behave in a slightly different way to CTAB/metMb because of their special structure. In contrast, no interaction is evident between the zwitterionic surfactant over a large range of concentrations because of the neutral charge of CHAPS, which precludes an effective electrostatic attraction between the ionic sites of CHAPS and a protein. The significant distance between the ionic sites with opposite charges in metMb precludes a double ionic interaction for each CHAPS surfactant molecule despite the presence of two oppositely charged ionic sites in the CHAPS molecule. Therefore, proteins interact with surfactants in multifarious ways and this depends on the surfactant species, concentration, and structure.