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題 名 | Properties of Lipid Bilayers Deduced from Hydration Dependence by X-ray Diffraction=藉由X光繞射測量不同水合程度脂膜以獲取磷質雙層膜的性質 |
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作 者 | 洪偉清; | 書刊名 | 黃埔學報 |
卷 期 | 50 民95.03 |
頁 次 | 頁125-145 |
分類號 | 361.191 |
關鍵詞 | 脂質雙層膜; 片層X光繞射; 膠體態; 流體態; 電子密度分佈圖; DMPC; DLPC; X-ray diffraction; Membrane tension; Hydrophobic interface; |
語 文 | 英文(English) |
中文摘要 | 我們利用片層x 光繞射測量單一指向多片層結構的DMPC 與DLPC 脂膜,並利用蒸汽壓以精確的控制脂膜的水含量。實驗上將樣品控制在固定的溫度上,並以繞射圖一系列的紀錄相對濕度由5% 到 98% 的結果,其範圍包含膠體態(gel phase)和流體態(fluid phase)。在膠體態時,由電子密度分佈圖的兩邊可各獲得一個高電子密度分佈的主峰及一個次峰,這兩峰間的距離Ih 在不同脂膜及不同濕度下的測量,顯示為一定值。甚至延伸至水合相變後的流體態,亦顯示出相同的距離Ih= 4.85Å.。將實驗結果與垂直入射懸浮 DMPC 脂膜的繞射結果及脂質分子結晶結構圖作比較,使我們得以證明電子密度分佈圖中的次峰即為脂質分子親水區與厭水區的界面所在。這結果不但可支持先前的研究學者如McIntosh and Simon 和Nagle 研究群所提出測量厭水區厚度Dc 的近似法是可接受的,也提供一個實際的實驗佐證。我們利用這個方法可精確的測量出厭水區厚度的改變,進而獲得脂膜的彈性性質,這也是探討蛋白質與脂膜作用的重要參數。由文獻的研究發現對於脂質分子的截面積量測相關結果,尤其是對於脂膜的橫向的壓縮性質的研究,在理論上與實驗上仍有明顯的爭議存在。因此我們對此提出一個新理論並藉由實驗來驗證以支持此理論。 |
英文摘要 | We measured x-ray lamellar diffraction of DMPC and DLPC in the form of oriented multilayers, with their water contents carefully controlled by vapor pressure. Consistent diffraction patterns were recorded along isotherms with the relative humidity varied from ~5% to ~98% covering both the gel phase and the fluid phase. In the gel phase, each side of the electron density profile showed a main peak and a secondary peak. The separation In between the two peaks is the same in both lipids and constant throughout the gel phase. The same two peaks also appear upon phase transition to the fluid phase with the same peak separation Ih=4.85Å. Comparisons with in-plane diffraction of freely suspended DMPC films and with crystallographic data allowed us to identify the secondary peak as the location of the hydrophilic-hydrophobic interface. This result supports the previous approach taken by McIntosh and Simon, and by Nagle et al to measure the thickness of the hydrophobic region Dc. This approach allows a precise measurement of the variation of Dc, which determine the elastic properties of lipid bilayers and is an important quantity describing protein-membrane interactions. We discussed the measurement of the area per lipid based on existing experimental evidence, and found that there are considerable uncertainties. We found both theoretical and experimental difficulties with previous theories for the lateral compressibility of lipid bilayers. We propose a new theory for the compressibility and suggest experiments to test it. |
本系統中英文摘要資訊取自各篇刊載內容。