生物膜含有由特定的脂質及蛋白質所構成的區塊(domains)，許多證據暗示著脂質浮排(lipid rafts)這種特殊的區塊在許多生物過程中扮演重要的角色。脂質浮排含有豐富的膽固醇(cholesterol)及抱合脂質(sphingolipids)，被認為是一種較周圍環境更有序的液晶態。我們運用氘核磁共振儀研究由1-palmitoyl-2-oleoyl-sn-glycerol- 3-phosphocholine (POPC)及膽固醇兩種成分所組成的人造細胞膜的構造及相行為。我們以氘取代POPC sn-1鏈上的氫，其測得的光譜會隨著膽固醇濃度及溫度而改變，研究發現，加入膽固醇會降低膠態(so phase)POPC膜的有序程度；然而會使得液態膜的碳鏈變得有序。分析兩種液晶態光譜暗示著當溫度高於膠態到液晶無序態(ld phase)的相變溫度時有兩種不同碳鏈結構的液態區域共存於很寬的膽固醇濃度及溫度範圍，此外，POPC/chol 溫度對膽固醇濃度的相圖其兩種液態共存區較DPPC/chol相圖寬，這結果暗示著POPC的不飽和碳鏈阻礙POPC與膽固醇間的交互作用致使POPC和膽固醇在液態的不相溶性大於DPPC/chol。 Biological membranes contain domains of distinct lipid and protein compositions. Accumulating evidence suggests that specialized domains, called lipid rafts, play important roles in many biological processes. Raft domains, rich in cholesterol and sphingolipids, are though to be in a more ordered liquid-crystalline phase than its surroundings. We investigate the membrane structure and phase behavior of model membrane composed of 1-palmitoyl-2-oleoyl-sn- glycero-3-phosphocholine (POPC) and cholesterol bilayers using deuterium nuclear magnetic resonance (2H NMR). The sn-1 chain of POPC was perdeuterated and spectra were taken as a function of cholesterol concentration and temperature. It is found that addition of cholesterol decreases the order of the so-phase POPC membranes, whereas increases the chain order of the liquid-phase POPC membranes. Analysis of the liquid crystalline spectra suggests that two types of liquid crystalline domains, having distinct average chain conformations, coexist over wide cholesterol concentration and temperature ranges above the so-to-ld transition temperature of POPC membranes. Furthermore, the temperature-composition phase diagram of POPC/chol exhibits a considerably broader two-liquid-phase region than DPPC/chol [1]. This suggests that the unsaturated chain of POPC hinders the interaction of POPC with cholesterol, such than liquid-liquid immiscibility in POPC/chol occurs over a larger composition range than in DPPC/chol membranes.
