在生物膜存在橫向異質的特性，這些異質的特性是指膜中有各種的脂質區塊。這些區塊中的脂質與蛋白質的組成成分及物理特性都不同。近期研究表示除了膽固醇外，其他固醇:例如麥胚固醇(β-sitosterol)也能引導產生出這脂質區塊，這些脂質區塊稱之為脂質浮排(lipid raft)。麥胚固醇為植物固醇的一種，其化學結構與膽固醇相近，過去研究重點著重於膽固醇而較少探討植物性固醇。文獻上發現在生物體內麥胚固醇能降低膽固醇的在血管中濃度並且減少心血管疾病的發生。我們使用氘核磁共振儀(2H NMR)研究麥胚固醇與DPPC人造細胞膜的物理特性。其方法為將DPPC上sn-1的氫代換成氘，觀察不同溫度與麥胚固醇的濃度變化所得到的光譜圖。結果顯示，麥胚固醇有不同影響於不同相位的DPPC膜。麥胚固醇能降低在相變溫度之下DPPC膜的有序程度；然而卻增加相變溫度之上DPPC膜的有序程度。我們可以從核磁共振光譜圖得到DPPC-d31/β-sitosterol膜的部分相圖，此部分相圖具有so+ld phase，so+lo phase和lo+ld phase三個兩相共存區域與一條三相共存線。 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. Recent evidence suggests that not only cholesterol, the major sterol found in mammals, but other sterols such as β-sitosterol are important for the formation of a specific domain called lipid raft. β-sitosterol is one of plant sterols and its chemical structure is similar to that of cholesterol. While most study of lipid-sterol interaction focuses on cholesterol, little is known about plane sterols. In addition, it is pointed out that β-sitosterol decreases serum of cholesterol and reduced cardiovascular disease. We investigate the phase behavior of model membranes composed of 1, 2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and β-sitosterol using deuterium nuclear magnetic resonance (2H NMR). The sn-1 chain of DPPC is deuterium labeled. The 2H NMR spectra were taken as a function of temperature and β-sitosterol concentration. Our data shows that addition of β-sitosterol promotes the formation of the lo phase. Moreover, β-sitosterol has opposite ordering effect on the DPPC membranes below and above Tm: It decreases the order of DPPC membranes below Tm, whereas increases the chain orders of DPPC above Tm. Finally, the partial phase diagram is determined from 2H NMR spectra. Coexistence of so+ld phase is observed at low β-sitosterol concentration. On the other hand, there are two two-phase coexistence regions, so+lo and lo+ld, found below and above Tm, respectively, at intermediated β-sitosterol concentration. A three-phase line separates these two regions is observed at 37°C.
