HYDROPHOBIC BARRIERS OF LIPID BILAYER-MEMBRANES FORMED BY REDUCTION OF WATER PENETRATION BY ALKYL CHAIN UNSATURATION AND CHOLESTEROL
HYDROPHOBIC BARRIERS OF LIPID BILAYER-MEMBRANES FORMED BY REDUCTION OF WATER PENETRATION BY ALKYL CHAIN UNSATURATION AND CHOLESTEROL
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DOI：
10.1021/bi00190a022
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发表时间：
1994-06-21
期刊：
影响因子：
2.9
通讯作者：
KUSUMI, A
中科院分区：
文献类型：
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作者：
SUBCZYNSKI, WK;WISNIEWSKA, A;KUSUMI, A
在冷冻脂质体悬浮液和液相膜中，评估了跨磷脂酰胆碱(PC)-胆固醇双层膜的疏水性分布作为烷基链长、不饱和度和胆固醇摩尔分数的函数。一系列硬脂酸自旋标记，探针贴在烷链上的不同位置，胆固醇类自旋标记(胆甾烷和雄烷自旋标记)，以及TEMPO-PC被用来检测局部疏水性随深度的变化，这是由水渗透到膜的程度决定的。主要通过在-150℃的冷冻悬浮液中观察氮氧化物自旋探针的超精细相互作用张量(A(Z))的z分量来监测局部疏水性，并通过饱和恢复ESR观察Fe(CN)(6)(3-)与膜中自旋探针的碰撞速率来进一步证实在流体相中的局部疏水性。饱和PC膜在整个膜上表现出低疏水性(高极性)，与异丙醇和正辛醇相当，即使在膜中心疏水性最高的地方也是如此。较长的烷基链只会使中心疏水性区域变宽，而不会增加疏水性水平。C9-C10双键的引入降低了膜中所有位置的水渗透水平，并且这种影响比顺式构型比反式构型大得多。胆固醇(30mol%)的加入极大地改变了膜的轮廓；对于饱和和不饱和的PC膜，它将从极性头基区的疏水性降低到大约C7和C9的深度，这大约是胆固醇的坚硬的类固醇环结构在膜中达到的位置。从甲醇水平到纯正己烷水平，膜的疏水性在这些位置急剧增加，在膜的内部区域疏水性保持不变。因此，形成有效的疏水屏障渗透小的极性分子需要烷基链不饱和和/或胆固醇。这种矩形疏水屏障的厚度小于碳氢化合物区域厚度的50%。在二油酰基-PC-胆固醇膜中得到的结果与在冷冻膜中得到的结果相似。这些结果与文献中水和氨基酸的渗透性数据有很好的相关性。
The hydrophobicity profiles across phosphatidylcholine (PC)-cholesterol bilayer membranes were estimated in both frozen liposome suspensions and fluid-phase membranes as a function of alkyl chain length, unsaturation, and cholesterol mole fraction. A series of stearic acid spin labels, with the probe attached to various positions along the alkyl chain, cholesterol-type spin labels (cholestane and androstane spin labels), and Tempo-PC were used to examine depth-dependent changes in local hydrophobicity, which is determined by the extent of water penetration into the membrane. Local hydrophobicity was monitored primarily by observing the z component of the hyperfine interaction tenser (A(z)) of the nitroxide spin probe in a frozen suspension of the membrane at -150 degrees C and was further confirmed in the fluid phase by observing the rate of collision of Fe(CN)(6)(3-) with the spin probe in the membrane using saturation recovery ESR. Saturated-PC membranes show low hydrophobicity (high polarity) across the membrane, comparable to 2-propanol and 1-octanol, even at the membrane center where hydrophobicity is highest. Longer alkyl chains only make the central hydrophobic regions wider without increasing the level of hydrophobicity. Introduction of a double bond at C9-C10 decreases the level of water penetration at all locations in the membrane, and this effect is considerably greater than the cis configuration than with the trans configuration. Incorporation of cholesterol (30 mol %) dramatically changes the profiles; it decreases hydrophobicity (increases water penetration) from the polar headgroup region to a depth of approximately C7 and C9 for saturated- and unsaturated-PC membranes, respectively, which is about where the bulky rigid steroid ring structure of cholesterol reaches in the membrane. Membrane hydrophobicity sharply increases at these positions from the level of methanol to the level of pure hexane, and hydrophobicity is constant in the inner region of the membrane. Thus, formation of effective hydrophobic barriers to permeation of small polar molecules requires alkyl chain unsaturation and/or cholesterol. The thickness of this rectangular hydrophobic barrier is less than 50% of the thickness of the hydrocarbon regions. Results obtained in dioleoyl-PC-cholesterol membranes in the fluid phase are similar to those obtained in frozen membranes. These results correlate well with permeability data for water and amino acids in the literature.