人造細胞膜中的液態區塊(liquid domain)常被當成研究細胞膜上脂質浮排(lipid raft)的模型。研究指出細胞膜處於液相有序(liquid order-lo)及液相無序(liquid disorder-ld) 的共存態，而 lo 態大部份由具有高相變溫度(melting temperature-Tm)的脂質分子及固醇類(sterol)所構成，ld 態大部份由具低相變溫度的脂質分子組成。本論文中利用核磁共振儀(2H-NMR)研究由高相變溫度脂質分子 DPPC，低相變溫度脂質分子 POPC，及固朜類麥角固醇(ergosterol)或膽固醇(cholesterol)所組成的人造細胞膜的相行為及特性。為了觀察每種脂質分子，POPC 及 DPPC 的碳鏈分別以氘分子標示，隨著溫度增加，擷取 NMR 光譜訊號。 我們的結果顯示在所研究的二種或三種成份組成的細胞膜中，DPPC 碳鏈的有序程度都比 POPC 高。在 1:1 DPPC/POPC 細胞膜中，我們觀察到在特定的溫度區間內存在 so 及 ld 態混合相。在含固醇的膜中，我們發現會促使 lo 相的生成，而脂質-膽固醇的交互作用比脂質-麥角固醇的交互作用強。另外，麥角固醇對脂質間交互作用的影響也不如膽固醇的影響大。膽固醇明顯地增進 DPPC-POPC 間的交互作用且此類經由膽固醇而產生的交互作用在含膽固醇的膜中相當重要。 Liquid domains in model membranes are frequently studied as models of lipid raft domain in plasma membrane. Studies show that membrane is in lo+ld phase coexistence that lo phase is believed to enrich in sterol and high melting-temperature (Tm) lipid while ld phase is formed by low Tm lipid. In this work, we study the phase behaviors and properties of binary and ternary mixture containing Dipalmitoyl- phosphatidylcholine (DPPC) as high Tm lipid, Palmitoyloleoylphosphatidylcholine (POPC) as low Tm lipid, and ergosterol or cholesterol as sterol using 2H-NMR. For the experiment, POPC and DPPC are deuterium-labeled in turn, such that information regarding each lipid component can be obtained. NMR spectra were taken as a function of temperature. The result shows that the chain order of DPPC is greater than that of POPC in all mixtures studied. In 1:1 DPPC/POPC binary mixture, so+ld phase coexistence is observed in a wide temperature range. The presence of sterol promotes the formation of lo phase in ternary mixtures. Lipid-cholesterol interactions are stronger than lipid-ergosterol interactions within 1:1:1 DPPC/POPC/sterol. Furthermore, the influence of ergosterol on the lipid-lipid interactions is not as robust as that of cholesterol. Cholesterol enhances the DPPC-POPC interaction significantly and super exchange coupling between DPPC and POPC via cholesterol is important.
