Hatfield R M, Fung L W
Department of Chemistry, Loyola University of Chicago, Illinois 60626.
Biophys J. 1995 Jan;68(1):196-207. doi: 10.1016/S0006-3495(95)80175-X.
Stratum corneum lipids are relatively complex, and there is little detailed understanding of their chemical and physical properties at the molecular level. Large unilamellar vesicles (LUVs) with lipid compositions similar to those of stratum corneum were prepared at pH 9 with commercially available lipids. This system was used as a model system for molecular studies of stratum corneum lipids. LUVs were chosen as the model system as they are comparatively more stable and can be characterized more quantitatively in terms of lipid concentration, surface area, and volume than model systems such as lipid mixture suspensions, lipid films, and small unilamellar vesicles. Results from freeze-fracture and cryo electron microscopy studies of our LUVs showed spherical vesicles. Quasi-elastic light scattering measurements revealed a narrow size distribution, centering around 119 nm. At room temperature, the LUVs were stable for several weeks at pH 9 and for more than 15 h but less than 24 h at pH 6. Differential scanning calorimetry measurements indicated broad endothermic transitions centered near 60-65 degrees C, closely matching the transition temperature reported for stratum corneum lipid extracts. Spin probes, 5-doxylstearic acid and 12-doxylstearic acid, were used for electron paramagnetic resonance (EPR) studies of the molecular dynamics of the lipids. EPR results indicated more restricted motion near the polar headgroup region than near the center of the alkyl chain region. Motional profiles of the spin labels near the polar headgroup and within the alkyl chain region in the LUVs were obtained as a function of temperature, ranging from 25 to 90 degrees C. We also found that the partitioning between the lipid and aqueous phases for each spin probe was temperature dependent and was generally correlated with phase transitions observed by differential scanning calorimetry and with alkyl chain mobility observed by EPR. Thus, this LUV system is well suited for additional molecular studies under different experimental conditions.
角质层脂质相对复杂，目前在分子水平上对其化学和物理性质的详细了解较少。使用市售脂质在pH 9条件下制备了脂质组成与角质层相似的大单层囊泡（LUVs）。该系统被用作角质层脂质分子研究的模型系统。选择LUVs作为模型系统是因为它们相对更稳定，并且与脂质混合物悬浮液、脂质膜和小单层囊泡等模型系统相比，可以在脂质浓度、表面积和体积方面进行更定量的表征。对我们制备的LUVs进行冷冻断裂和冷冻电子显微镜研究的结果显示为球形囊泡。准弹性光散射测量揭示了窄的尺寸分布，中心约为119 nm。在室温下，LUVs在pH 9时可稳定数周，在pH 6时可稳定超过15小时但少于24小时。差示扫描量热法测量表明，宽的吸热转变集中在60 - 65摄氏度附近，与角质层脂质提取物报道的转变温度密切匹配。自旋探针5 - 脱氧硬脂酸和12 - 脱氧硬脂酸用于脂质分子动力学的电子顺磁共振（EPR）研究。EPR结果表明，极性头部基团区域附近的运动比烷基链区域中心附近的运动更受限制。获得了LUVs中极性头部基团附近和烷基链区域内自旋标记的运动轮廓随温度的变化情况，温度范围为25至90摄氏度。我们还发现，每个自旋探针在脂质相和水相之间的分配取决于温度，并且通常与差示扫描量热法观察到的相变以及EPR观察到的烷基链流动性相关。因此，这个LUV系统非常适合在不同实验条件下进行额外的分子研究。
