Effect of fatty acyl chain length and structure on the lamellar gel to liquid-crystalline and lamellar to reversed hexagonal phase transitions of aqueous phosphatidylethanolamine dispersions.
Effect of fatty acyl chain length and structure on the lamellar gel to liquid-crystalline and lamellar to reversed hexagonal phase transitions of aqueous phosphatidylethanolamine dispersions.
复制标题
脂肪酰链长度和结构对磷脂酰乙醇胺水分散体的层状凝胶到液晶以及层状到反六方相变的影响。
DOI：
10.1021/bi00428a020
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发表时间：
1989
期刊：
影响因子：
2.9
通讯作者：
Gruner,SM
中科院分区：
文献类型：
--
作者：
Lewis,RN;Mannock,DA;McElhaney,RN;Turner,DC;Gruner,SM
物理系，普林斯顿大学，普林斯顿，新泽西08540接收于1988年6月6日;修订的Mandarin pt接收于1988年8月24日摘要：本文研究了一系列合成磷脂酰乙醇胺水分散液的层状凝胶/液晶和层状液晶/反六方相转变，用差示扫描量热法、~（31）P核磁共振谱和X射线衍射研究了不同长度的脂环族脂肪酰基链。对于任何给定的含有单一化学类别的脂肪酸的磷脂酰乙醇胺的同源系列，层状凝胶/液晶相转变温度增加，层状液晶/反向六方相转变温度随着烃链长度的增加而降低。对于一系列具有相同烃链长度但具有不同化学结构的磷脂酰乙醇胺，层状凝胶/液晶和层状液晶/反六方相转变温度均在相同方向上显著变化。特别地，在相当的有效烃链长度下，层状凝胶/液晶和层状液晶/反六方相转变温度平行变化，使得这两个相转变之间的温度差几乎恒定。此外，在可比较的有效酰基链长度下，层状液晶相和反六方相的d间距都是相似的，这意味着磷脂酰乙醇胺双层在层状液晶/反六方相转变开始时的厚度和水-在该相变完成时形成的填充圆柱体是可比较的，并且与酰基链的化学结构无关。这些结果表明，对于任何给定的烃链长度，可能有一个临界厚度，在该临界厚度下，液晶磷脂酰乙醇胺双层变得不稳定，相对于反转的非双层相，如Hn相，并且达到该临界厚度的温度取决于该双层接近烃链熔融相变温度。迄今为止研究的所有生物膜的脂质似乎在生理相关的温度和水合条件下完全或几乎完全以层状或双层状态存在[参见Singer和Nicolson（1972）和McElhaney（1984）]。然而，许多生物膜含有一种或多种脂质组分，其在分离时优选以非双层状态存在[参见Cullis et al.（1983），Kazfors et al.（1984）和Gruner et al.（1985）]。虽然非双层形成磷脂和糖脂在某些生物膜中占膜脂总量的很大比例，但目前这类脂质的生物学功能尚不清楚。一些工作者已经假设，由这种非双层形成脂质诱导的非层状结构的瞬时形成可以在诸如膜融合的过程中起关键作用（Verkleij等人，1979; Siegel，1986 a，B）或在离子和大分子的跨膜运动中（Cullis等，1983年）。然而，其他工作者认为，在生物膜中实际形成非层状脂质结构是不可能的，非-+的作用这项工作得到了加拿大医学研究理事会（RNM）的操作和主要设备赠款的支持，由博士后研究奖学金（DAM）和主要设备赠款。
Department of Physics, Princeton University, Princeton, New Jersey 08540 Received June 6, 1988; Revised Manuscript Received August 24, 1988 abstract: The lamellargel/liquid-crystalline and the lamellar liquid-crystalline/reversed hexagonal phase transitions of aqueous dispersions of a number of synthetic phosphatidylethanolamines containing linear saturated, branched chain, and alicyclic fatty acyl chains of varying length were studied by differential scanning calorimetry, 31P nuclear magnetic resonance spectroscopy, and X-ray diffraction. For any given homologous series of phosphatidylethanolamines containing a single chemical class of fatty acids, the lamellar gel/liquid-crystalline phase transition temperature increases and the lamellar liquid-crystalline/reversed hexagonal phase transition temperature decreases with increases in hydrocarbon chain length. For a series of phosphatidylethanolamines of the same hydrocarbon chain length but with different chemical structures, both the lamellar gel/liquid-crystalline and the lamellar liquid-crystalline/reversed hexagonal phase transition temperatures vary markedly and in the same direction. In particular, at comparable effective hydrocarbon chain lengths, both the lamellar gel/liquid-crystalline and the lamellar liquid-crystalline/reversed hexagonal phase transition temperatures vary in parallel, such that the temperature difference between these two phase transitions is nearly constant. Moreover, at comparable effective acyl chain lengths, the d spacings of the lamellar liquid-crystalline phases and of the inverted hexagonal phases are all similar, implying that the thickness of the phosphatidylethanolamine bilayers at the onset of the lamellar liquid-crystalline/reversed hexagonal phase transition and the diameter of the water-filled cylinders formed at the completion of this phase transition are comparable and independent of the chemical structure of the acyl chain. These results suggest that for any given hydrocarbon chain length, there may be a critical thickness at which the liquid-crystalline phosphatidylethanolamine bilayer becomes unstable with respect to inverted nonbilayer phases such as the Hn phase and that the temperature at which this critical thickness is reached is dependent upon that bilayers proximity to the hydrocarbon chain-melting phase transition temperature. e lipids of all biological membranes studied to date appear to exist exclusively or nearly exclusively in the lamellar or bilayer state under physiologically relevant conditions of temperature and hydration [see Singer and Nicolson (1972) and McElhaney (1984)]. Nevertheless, many biological membranes contain one or more lipid components which, in isolation, prefer to exist in a nonbilayer state [see Cullis et al.(1983), Rilfors et al.(1984), and Gruner et al.(1985)]. Although non-bilayer-forming phospho-and glycolipids com-prise a significant fraction of the total membrane lipids in some biological membranes, the biological functions of such lipids remain unclear at present. Some workers have postulated that the transient formation of nonlamellarstructures induced by such non-bilayer-forming lipids could play a key role in pro-cesses such as membrane fusion (Verkleij et al., 1979; Siegel, 1986a, b) or in the transmembrane movement of ions and macromolecules (Cullis et al., 1983). Other workers, however, argue that the actual formation of nonlamellar lipid structures in biological membranes is unlikely and that the role of non-+ This work was supported by operating and major equipment grants from the Medical Research Council of Canada (RNM), by a post-doctoral research fellowship (DAM) and major equipment grants from the …