Wang Z Q, Lin H N, Li S, Huang C H
Department of Biochemistry, University of Virginia, Charlottesville 22908.
J Biol Chem. 1994 Sep 23;269(38):23491-9.
This investigation was designed to determine how information about the lipid chain melting and structural characteristics of sn-1 saturated/sn-2 monounsaturated phosphatidylethanolamines, a subclass of naturally occurring phospholipids, can be generalized among these lipid molecules. Specifically, 30 molecular species of sn-1 saturated/sn-2 unsaturated monoenoic phosphatidylethanolamines were semi-synthesized. The phase transition behavior of these monoenoic lipids in excess water was studied calorimetrically. The computer-based molecular mechanics approach was used to simulate the energy-minimized structures and to calculate steric energies for the diglyceride moieties of some of the 30 monoenoic lipid molecules, at T < Tm, in various aggregated states. These combined calorimetric and computational studies led to the following results and conclusions. 1) For a homologous series of monoenoic lipids with a common molecular weight and with a cis-double bond at various positions along the sn-2 acyl chain, the characteristic reduction of the main phase transition temperature (Tm) is proposed to be a result of an entropy-driven phenomenon. 2) The maximal decrease in the Tm for bilayers prepared from four series of monoenoic phosphatidylethanolamines containing a sn-2 octadecenoyl chain is shown by interpolation of calorimetric data to occur uniquely when the cis double bond is located commonly between C(10) and C(11) positions from the carboxyl end. 3) Monoenoic phosphatidylethanolamines can be divided into two groups. The Tm values obtained with bilayers of monoenoic lipids within each group can be systematically correlated with their structural parameters, leading to the derivation of two general Tm-structure relationships.
本研究旨在确定关于sn-1饱和/sn-2单不饱和磷脂酰乙醇胺（一种天然存在的磷脂亚类）的脂链熔化和结构特征的信息如何在这些脂质分子中进行归纳。具体而言，半合成了30种sn-1饱和/sn-2不饱和单烯磷脂酰乙醇胺分子种类。通过量热法研究了这些单烯脂质在过量水中的相变行为。使用基于计算机的分子力学方法来模拟能量最小化结构，并计算30种单烯脂质分子中某些分子的甘油二酯部分在T < Tm时处于各种聚集状态下的空间能。这些量热和计算研究相结合得出了以下结果和结论。1）对于一系列具有相同分子量且在sn-2酰基链上不同位置具有顺式双键的单烯脂质，主相变温度（Tm）的特征性降低被认为是熵驱动现象的结果。2）通过量热数据插值显示，由四个含有sn-2十八碳烯酰链的单烯磷脂酰乙醇胺系列制备的双层膜中，Tm的最大降低独特地发生在顺式双键通常位于羧基端的C(10)和C(11)位置之间时。3）单烯磷脂酰乙醇胺可分为两组。每组内单烯脂质双层膜获得的Tm值可以与其结构参数进行系统关联，从而得出两种通用的Tm-结构关系。
