Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria.
Biophys Chem. 2010 Aug;150(1-3):129-35. doi: 10.1016/j.bpc.2010.04.004. Epub 2010 Apr 22.
Phosphatidylglycerol and cardiolipin represent the most abundant anionic phospholipid components of cytoplasmic bacterial membranes and thus are used as constituents for membrane mimetic systems. In this study, we have characterized the temperature dependent phase behaviour of the binary system dipalmitoyl-phosphatidylglycerol (DPPG) and tetramyristoyl-cardiolipin (TMCL) using microcalorimetry and X-ray scattering techniques. Both lipids exhibited a very similar main transition temperature ( approximately 41 degrees C), showing a minimum (39.4 degrees C) for the binary mixtures at X(DPPG)=0.8, and exhibited low-temperature phase transitions, which were abolished by incorporation of small amounts (<or=10mol%) of the other lipid component. Therefore, over a wide temperature and composition range a lamellar L(beta) gel phase is the predominant structure below the chain melting transition, characterized by a relatively broad wide-angle peak for X(DPPG)<or=0.8. This observation suggests the existence of packing inconsistencies of the TMCL/DPPG hydrocarbon lattices in the gel phase, supported by the small average size of lipid clusters ( approximately 50 lipids) within this composition range. The bilayer thickness for the lamellar-gel phase showed a monotonic increase (56A for TMCL to about 58A for X(DPPG)=0.8 at 30 degrees C), which may be explained by different degrees of partial interdigitation of the acyl chains to compensate for the differences in the hydrocarbon lengths of DPPG and TMCL in the L(beta) phase.
磷脂酰甘油和心磷脂是细胞质细菌膜中最丰富的阴离子磷脂成分，因此被用作膜模拟系统的组成部分。在这项研究中，我们使用微量热法和 X 射线散射技术表征了二棕榈酰磷脂酰甘油（DPPG）和四肉豆蔻酰心磷脂（TMCL）的二元体系随温度的相行为。这两种脂质都表现出非常相似的主相变温度（约 41°C），在 X（DPPG）=0.8 的二元混合物中表现出最低值（39.4°C），并且表现出低温相变，这被少量（≤10mol%）其他脂质成分的掺入所消除。因此，在较宽的温度和组成范围内，层状 L（β）凝胶相是链熔融转变以下的主要结构，其特征是广角宽峰较宽，X（DPPG）≤0.8。这种观察结果表明，在凝胶相中 TMCL/DPPG 烃晶格的堆积不一致性存在，这得到了在该组成范围内脂质簇的平均大小（约 50 个脂质）较小的支持。层状-凝胶相的双层厚度呈单调增加（TMCL 为 56A，X（DPPG）=0.8 时约为 58A，温度为 30°C），这可以通过酰链的不同程度的部分互贯来解释，以补偿 L（β）相中 DPPG 和 TMCL 烃链长度的差异。
