SHAPE OF HYDROPHOBIC BARRIER OF PHOSPHOLIPID BILAYERS (EVIDENCE FOR WATER PENETRATION IN BIOLOGICAL-MEMBRANES)
SHAPE OF HYDROPHOBIC BARRIER OF PHOSPHOLIPID BILAYERS (EVIDENCE FOR WATER PENETRATION IN BIOLOGICAL-MEMBRANES)
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DOI：
10.1007/bf01870086
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发表时间：
1974-01-01
影响因子：
2.4
通讯作者：
VAN, SP
中科院分区：
文献类型：
--
作者：
GRIFFITH, OH;DEHLINGER, PJ;VAN, SP
以前的工作表明，有一个小的溶剂效应的氮氧自旋标记物的电子自旋共振谱。本文的目的是开发溶剂效应的半定量处理，并使用这种处理来估计疏水屏障的形状（即，在这种溶剂效应的半定量处理中，对各向同性14 N偶合常数ΔA的总效应表示为与货车德瓦尔斯相互作用、氢键、磷脂极性基团的带电双层和膜电位相关的项的总和。作为电场函数的Δ A的大小用Hückel分子轨道理论估计，并独立地使用Onsager模型。利用这些关系，通过对二叔丁基氮氧自由基在33种溶剂中稀溶液的ESR测量和双电层电场和膜电位的计算，估算了各种溶剂效应项的相对重要性。4′，4′-二甲基恶唑烷-N-氧基）标记物沿脂链的不同位置沿着扩散到磷脂囊泡和膜（来自小牛肝微粒体组分）中。疏水屏障的形状被绘制为极性指数，该极性指数根据脂质自旋标记物的Δ A可操作地定义。带电双层的效果是不太重要的水渗透，除非当自旋标签是在几个埃的带电基团。膜电位对Δ A的任何影响都是微不足道的。ESR谱的比较表明，显着的水渗透到双层中发生在纯脂质双层和膜制剂。
Previous work has shown that there is a small solvent effect on the electron spin resonance spectra of nitroxide spin labels. The aim of this paper is to develop a semiquantitative treatment of the solvent effects and to use this treatment to estimate the shape of the hydrophobic barrier (i.e., polarity profile) of lipid bilayers.In this semiquantitative treatment of solvent effects, the total effect on the isotropic14N coupling constant, ΔA, is expressed as a sum of terms associated with van der Waals interactions, hydrogen bonding, the charged double layer of phospholipid polar groups and the membrane potential. The magnitude of ΔAas a function of the electric field is estimated with Hückel molecular orbital theory and, independently, using the Onsager model. With these relations, estimates of the relative importance of the various solvent effect terms are obtained from accurate ESR measurements on dilute solutions of di-t-butyl nitroxide in thirty-three solvents and calculations of the electric field produced by the charged double layer and the membrane potential.To estimate the shape of the hydrophobic barrier of lipid bilayers, fatty acids andl-α-lecithins with doxyl (i.e., 4′, 4′-dimethyloxazolidine-N-oxyl) labels bonded to various positions along the lipid chains were diffused into phospholipid vesicles and membranes (from the calf liver microsomal fraction). The shape of the hydrophobic barrier is plotted as a polarity index operationally defined in terms of the ΔAof the lipid spin labels. The effect of the charged double layers is less important than water penetration except when the spin label is within a few Angstroms of the charged groups. Any effects of a membrane potential on ΔAare insignificant. A comparison of ESR spectra indicates that significant water penetration into the bilayer occurs in both the pure lipid bilayers and in the membrane preparations.