Laser light scattering evidence for a common wormlike growth structure of mixed micelles in bile salt- and straight-chain detergent-phosphatidylcholine aqueous systems: Relevance to the micellar structure of bile
Laser light scattering evidence for a common wormlike growth structure of mixed micelles in bile salt- and straight-chain detergent-phosphatidylcholine aqueous systems: Relevance to the micellar structure of bile
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DOI：
10.1021/bi980182y
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发表时间：
1998-10-20
期刊：
影响因子：
2.9
通讯作者：
Carey, MC
中科院分区：
文献类型：
--
作者：
Cohen, DE;Thurston, GM;Carey, MC
我们采用准弹性和静态光散射的方法测量了胆盐（胆酸盐和牛磺酰脱氧胆酸盐，都是胆酰衍生物）和糖酰基链洗涤剂辛基葡萄糖苷的混合胶束溶液中的平均流体动力半径（R-h）（app）、分子量（M-app）和旋转半径（R-g）（app）的表观值，其中蛋黄磷脂酰胆碱（EYPC）是总脂浓度（0.1-10 g/dL）、EYPC/洗涤剂摩尔比（0-1.2）的函数。离子强度（0.15 ~ 0.3 M NaCl）在20℃和1atm下。当稀释接近混合胶束相边界时，（R-h）（app）、M-app和（R-g）（app）值显著增加，最高可达20倍。对于每个胶束体系，尽管总脂质浓度、洗涤剂分子种类和离子强度变化很大，但其结垢比（R-h）(app)/M-app（1/2）和（R-g）(app)/(R-h)（app）基本保持恒定，分别为0.018 nm/(g/mol)（1/2）和1.5（无量纲）。精细化的数据分析与胆盐-EYPC胶束的扁平“混合圆盘”模型不一致[Mazer， N. a, Benedek， G. B, and Carey， M. C. (1980) Biochemistry 19,601]和辛基葡萄糖苷-EYPC胶束的数值（R-h）（app/）M-app（1/2）对应于一个类似于1nm的假设圆盘厚度，比EYPC分子的双分子宽度小4倍，对于一个圆盘来说，在低总脂质浓度下，（R-g）(app)/(R-h)（app）比值应接近1。假设胶束呈圆盘状，我们发现胶束间排除的体积相互作用对M-app只有很小的影响，并且不能解释不切实际的磁盘厚度。相反，局部圆柱形、半柔性的虫状胶束直径d = 4 nm，在溶液中持续长度xi(p) = 17 nm，与观察到的（R-h）(app)/M-app（1/2）和（R-g）(app)/(R-h)（app）值兼容。当EYPC/taurochenodeoxycholate = 0.6和EYPC/cholate = 1.0时，在0.15 M NaCl中稀释和使用第二维里系数后，独立胶束生长[Egelhaaf， s.u, and Schurtenberger， P. (1994) J. Phys。化学，98,8560]足以估计胶束的重量。在0.4 M NaCl条件下，EYPC/胆酸盐= 1.0，在0.15 M NaCl条件下，EYPC/胆酸盐= 1.2，在0.15 M NaCl条件下，EYPC/辛基葡萄糖苷= 0.13，这些体系都能形成高度重叠的半稀聚合物溶液，模拟了观察到的结垢比。在这种半稀体系中，仅使用第二维里系数来解释胶束间的相互作用是不足以估计胶束重量的。本研究的结果，结合高稀释时已知的三元胆盐- eypc -水相图的相界位置，表明在接近胶束相极限的浓度下，可能会发生蠕虫状混合胶束的延伸和缠结。
We employed quasielastic and static light scattering to measure apparent values of the mean hydrodynamic radii (R-h)(app), molecular weights (M-app), and radii of gyration (R-g)(app) in solutions containing mixed micelles composed of bile salts (cholate and taurochenodeoxycholate, both cholanoyl derivatives) and the glycoacyl chain detergent, octyl glucoside, with egg yolk phosphatidylcholine (EYPC) as functions of total lipid concentration (0.1-10 g/dL), EYPC/detergent molar ratio (0-1.2), and ionic strength (0.15-0.3 M NaCl) at 20 degrees C and 1 atm. As the mixed micellar phase boundaries were approached by dilution, (R-h)(app), M-app, and (R-g)(app) values increased markedly by up to 20-fold. For each micellar system, the scaling ratios (R-h)(app)/M-app(1/2) and (R-g)(app)/(R-h)(app) remained essentially constant at 0.018 nm/(g/mol)(1/2) and 1.5 (dimensionless), respectively, despite large variations in total lipid concentration, detergent molecular species, and ionic strength. Refined data analysis is inconsistent with a flat "mixed-disc" model for bile salt-EYPC micelles [Mazer, N. A,, Benedek, G. B., and Carey, M. C. (1980) Biochemistry 19, 601] and octyl glucoside-EYPC micelles principally because the numerical value of (R-h)(app/)M-app(1/2) corresponds to a hypothetical disk thickness of similar to 1 nm, which is 4-fold smaller than the bimolecular width of EYPC molecules, and for a disk, (R-g)(app)/(R-h)(app) ratios should be close to 1 at low total lipid concentrations. Assuming disc-shaped micelles, we show that intermicellar excluded volume interactions would have only a minor effect on M-app, and cannot account for the unrealistic disk thickness. instead, locally cylindrical, semiflexible wormlike micelles of diameter d = 4 nm and persistence length xi(p) = 17 nm in solution are compatible with the observed (R-h)(app)/M-app(1/2) and (R-g)(app)/(R-h)(app) values when intermicellar excluded-volume interactions are considered. With EYPC/taurochenodeoxycholate = 0.6 and EYPC/cholate = 1.0 in 0.15 M NaCl, independent micelles grow upon dilution and use of the second virial coefficient [Egelhaaf, S. U., and Schurtenberger, P. (1994) J. Phys. Chem. 98, 8560] is adequate for estimating micellar weights. The systems EYPC/cholate = 1.0 in 0.4 M NaCl, EYPC/cholate = 1.2 in 0.15 M NaCl, and EYPC/octyl glucoside = 0.13 in 0.15 M NaCl all form highly overlapping, semidilute polymer solutions, which mimic the observed scaling ratios. In such semidilute systems, use of the second virial coefficient alone to account for intermicellar interactions is inadequate for estimating micellar weights. The results of the present study, in combination with locations of known phase boundaries of the ternary bile salt-EYPC-water phase diagram at high dilution, suggest that elongation, as well as entanglement of wormlike mixed micelles may occur at concentrations approaching the micellar phase limit.