The role of the side chain of sterols and the sterol ring structure on the formation of ordered phases of the type observed in membrane rafts has been examined in aqueous dispersions of binary mixtures of sphingomyelin and androsterol. Comparisons have been made with binary systems of cholesterol, stigmasterol, beta-sitosterol, and ergosterol with either sphingomyelin or dipalmitoylphosphatidylcholine. Thermotropic phase behaviour and structure of the mixed aqueous dispersions were characterized by differential scanning calorimetry, synchrotron X-ray diffraction, freeze-fracture electron microscopy, and Fourier-transform infrared spectroscopy. We show that: (i) Androsterol is less efficient in promoting the formation of liquid-ordered phase than other naturally occurring sterols which possess a side chain, (ii) cholesterol is the most efficient sterol of those investigated in forming liquid-ordered phase, (iii) the molecular stoichiometry of egg sphingomyelin and androsterol in the liquid-ordered phase is about 2:1, and (iv) sphingomyelin can form more stable liquid-ordered phase than glycerophospholipid in binary systems containing androsterol.

中文翻译：

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固醇环和侧链对鞘磷脂双层结构和相行为的作用。

在鞘磷脂和雄甾醇的二元混合物的水分散体中已经检查了固醇侧链和固醇环结构在膜筏中观察到的有序相的形成中的作用。已将胆固醇，豆甾醇，β-谷甾醇和麦角固醇与鞘磷脂或二棕榈酰磷脂酰胆碱的二元体系进行了比较。通过差示扫描量热法，同步加速器X射线衍射，冷冻断裂电子显微镜和傅里叶变换红外光谱对混合水分散体的热致相行为和结构进行了表征。我们证明：（i）雄甾醇比其他具有侧链的天然甾醇在促进液相有序相形成方面效率较低，