最近證據顯示，生物細胞膜的結構具有異質性。一般認為此種異質性是指細胞膜上存在著不同的脂質區塊，這些區塊具有不同的化學成分及物理性質。脂質浮排（lipid rafts, 一種富含膽固醇及抱合脂質區塊）被認為和許多重要的生物過程有關。含膽固醇的人造細胞膜的研究顯示，薄膜內有液相有序（lo）及液相無序（ld）兩相共存的情況產生。這兩種液相，是以碳氫鏈及橫向排列的有序程度來區分。ㄧ般認為，生物細胞膜上的脂質浮排即為人造細胞膜的lo 相區塊。然而，有些研究發現，生物細胞膜上所觀察到的脂質浮排的大小與人造細胞膜的lo 相區塊的大小有一段差距。這個差異也許是因為生物細胞膜上有蛋白質存在的緣故。在有些生物細胞膜中，膽固醇占了所有脂質含量的ㄧ半。我們研究含POPE 及麥角固醇 (ergosterol) 的人造細胞膜發現，當麥角固醇的含量很高時，POPE 碳氫鏈的有序程度隨著麥角固醇的增加而變弱。這個現象未曾在其他類似的人造細胞膜發現過。這個結果顯示當麥角固醇含量很高時，脂質-麥角固醇的交互作用比我們想像得複雜。我們想知道含脂質及膽固醇的人造細胞膜是否也有類似的結果。在這個計畫中我們將研究，加入浮排蛋白對處於ld 及lo 兩相共存時的人造細胞膜的影響。我們運用固態氘核磁共振(2H NMR)的技術來觀察人造細胞膜的相行為，並且用多種顯微技術來觀察人造細胞膜的形貌。另外我們也將運用固態氘核磁共振及傅利葉轉換紅外線光譜儀(FTIR)來研究固醇含量很高的人造細胞膜的物理特性。 ; Recent evidence suggests that lateral heterogeneities exist in biological membranes of living cell. The heterogeneity is proposed to be a coexistence of lipid domains with differing degrees of order, lipid/protein compositions, and physical properties in the membrane. The domains (lipid rafts) enriched in cholesterol and sphingolipid have been implicated to play important roles in a wide range of biological processes. Coexisting of liquid-ordered and liquid-disordered phases, differing in chain conformational and translational orders, has been observed in model membranes containing cholesterol. It is proposed that the lipid rafts observed in cell membranes correspond to the lo-phase domains in model membranes. However, there is a discrepancy in domain sizes obtained from model membranes and cell membranes. It is proposed that the proteins in cell membranes may play some role. Cholesterol comprises up to half of all the lipids in some plasma membranes. Our study of POPE/ergosterol up to 65 mol% shows that the lipid chain order exhibits interesting behavior: it decreases with increasing ergosterol at high concentration, which has not been observed in other lipid/sterol systems. This suggests that the lipid-ergosterol interaction seems to be complicated at high ergosterol concentration. It is of interest whether membranes containing cholesterol display similar behavior. We propose to investigate the evolution of ld and lo phase coexistence in lipid/sterol membranes with and without raft proteins. The phase behavior, obtained by 2H NMR, and the membrane morphology, obtained by various microscopic techniques, will be studied. In addition, the properties of lipid membranes containing high concentration of sterol (>40 mol%) will also be studied by 2H NMR and FTIR. ; 研究期間 9808 ~ 9907
