Rhodes D G, Blechner S L, Yager P, Schoen P E
Department of Radiology, University of Connecticut Health Center, Farmington 06032.
Chem Phys Lipids. 1988 Nov;49(1-2):39-47. doi: 10.1016/0009-3084(88)90062-x.
This report presents the first X-ray diffraction data on diacetylenic phospholipids. The tubule-forming polymerizable lipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC), was studied by low angle X-ray diffraction from partially dehydrated oriented multibilayers in both polymerized and unpolymerized form. Bilayers of this material were found to be highly ordered, yielding as many as 16 orders of lamellar diffraction, in both the polymerized and unpolymerized states. The unit cell dimension was very small for a lipid of this size. In addition to the features usually observed in the electron density profile structure of phospholipid bilayers, the electron-dense diacetylenic portions of the fatty acyl chain produced electron density maxima at two well-defined levels on each side of the bilayer approximately 15 A and 9 A from the bilayer midplane. A model molecular conformation deduced from the one-dimensional electron density map features all-trans acyl chains tilted at approximately 28 degrees from the bilayer normal that are interdigitated with chains of the opposing monolayer by approximately two carbons at the bilayer center. The linear diacetylene moieties on beta- and gamma-chains appear at different positions along the bilayer normal axis and are roughly parallel to the bilayer surface. This model is discussed in terms of a polymerization mechanism.
本报告展示了关于二乙炔基磷脂的首份X射线衍射数据。通过对部分脱水的取向多层膜进行低角度X射线衍射，研究了可形成微管的可聚合脂质1,2-双(10,12-二十三碳二炔酰基)-sn-甘油-3-磷酸胆碱(DC8,9PC)的聚合态和未聚合态。发现这种材料的双层在聚合态和未聚合态下都高度有序，产生多达16个层状衍射级次。对于这种大小的脂质来说，其晶胞尺寸非常小。除了磷脂双层电子密度分布结构中通常观察到的特征外，脂肪酰链的电子致密二乙炔部分在双层两侧距双层中平面约15 Å和9 Å的两个明确水平上产生电子密度最大值。从一维电子密度图推导的模型分子构象特征为：全反式酰链从双层法线倾斜约28度，在双层中心与相对单层的链相互交错约两个碳原子。β链和γ链上的线性二乙炔部分沿双层法线轴出现在不同位置，且大致平行于双层表面。根据聚合机理对该模型进行了讨论。
