| Summary: | 博士 === 國立中央大學 === 物理學系 === 104 === 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.
|
|---|
