固醇在生物膜的脂質組織及動力學性質扮演重要的角色。研究證實膜上富含膽固醇和磷鞘脂的脂筏區塊，在很多的生物功能的運作具有關鍵性的影響。然而，它們的存在和物理性質仍有爭議。為了對這些問題做深入的探討，我們研究飽和脂質、不飽和脂質、固醇組成的人造細胞膜的物理性質。研究中，我們運用螢光顯微術得到大型單層微胞(giant unilamellar vesicles)的形態隨溫度與成分的變化。由核磁共振(2H NMR)研究其人造細胞膜的相行為，進而建構該成分的相圖。結果顯示該三元混合物在相圖上不同的區域顯示不同的特性。例如，在固醇濃度較低的膠態與液態的共存區呈現微米尺度的小型分散的區塊(small, scattered domains)。而在固醇濃度較廣之液態-液態共存區,則形成微米尺度的大面積區塊(large domains)。 目前大多數研究聚焦於含低濃度(<30 mol%)固醇的脂質膜的探討，對於含高濃度固醇的脂質膜的研究相對較少。然而有些細胞膜中的膽固醇的濃度可以大於40 mol%。為了研究細胞膜中的高濃度固醇區域的物理性質，我們運用核磁共振光譜術與x-ray繞射研究脂質與固醇組成的人造細胞膜，我們發現相對於膽固醇分子結構，在碳氫鏈上額外的分子群與雙鍵，兩者皆阻礙了脂質與固醇之間的交互作用。另一方面，固醇環上額外的雙鍵對於脂質與固醇之間的交互作用並無影響。 ;Sterols play important roles on lipid organization and dynamics in cell membranes. Rafts domains rich in cholesterol and sphingolipids have been implicated to play crucial roles in a wide range of biological processes. However, their existence and physical properties have been controversial. To gain a better understanding of these issues, we study the physical properties of model membranes composed of saturated lipid, unsaturated lipid and sterol. The morphology of giant unilamellar vesicles has been observed as a function of temperature and composition by fluorescence microscopy. The phase behavior of model membranes was investigated by deuterium nuclear magnetic resonance (2H NMR) spectroscopy. The composition phase diagram was constructed. This ternary mixture manifests itself differently at different regions of the phase diagram. Solid-liquid phase coexistence, displaying small, scattered domains in micron size, was observed at low sterol concentration. Liquid-liquid phase coexistence, exhibiting large domains in micron size, was observed in a wide sterol concentration range. While most studies have been focused on membranes containing low sterol concentration (<30 mol %), less studies have been performed at the high sterol concentration. Cholesterol content can be as high as 40 mol % or greater in some cells. To investigate the physical properties of membranes at high sterol concentration regime, we study model membranes composed of lipid and sterol by 2H-NMR spectroscopy and x-ray diffraction. We found that in comparison with cholesterol, the extra group and extra double bond at the side chain of other sterols both hinder the lipid-sterol interaction. The extra double bond at the fuse ring, on the other hand, has no effect on the lipid-sterol interaction.
