Wu W G, Chi L M
Institute of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan, China.
Biochim Biophys Acta. 1990 Jul 24;1026(2):225-35. doi: 10.1016/0005-2736(90)90068-y.
13C-NMR spectra have been obtained at 50.3 MHz for monoarachidoylphosphatidylcholine (MAPC) and dipalmitoylphosphatidylcholine (DPPC) dispersions from 25 degrees C to 55 degrees C and for DPPC polycrystals at 25 degrees C using the cross polarization/magic angle spinning technique. Differential scanning calorimetric studies on DPPC and MAPC dispersions show comparable lipid phase transitions with transition temperatures at 41 degrees C and 45 degrees C, respectively, and thus enable the comparison of thermal, structural and dynamic differences between these two systems at corresponding temperatures. Conformational-dependent 13C chemical shift studies on DPPC dispersions demonstrate not only the coexistence of the tilted gel (L beta') and liquid-crystalline (L alpha) phases in the rippled gel (P beta') phase, but also the presence of an intermediate third microscopic phase as evidenced by three resolvable peaks for omega - 1 methylene carbon signals at the temperature interval between Tp and Tm. By comparing chemical shifts of MAPC in the hydrocarbon chain region with those of DPPC at similar reduced temperatures, it can be concluded that the packings are perturbed markedly in the middle segment of the fatty acyl chain during the lamellar to micellar transition. However, terminal methylene and methyl groups of interdigitated MAPC lamellae were found to be more ordered than those of non-interdigitated DPPC bilayers in the gel state. Interestingly, the terminal methyl groups of MAPC in the micelles remain to be relatively ordered; in fact, they are more ordered than the corresponding acyl chain end of DPPC in the liquid-crystalline state. Analysis of data obtained from rotating frame proton spin-lattice relaxation measurements shows a highly mobile phosphocholine headgroup, a rigid carbonyl group and an ordered hydrocarbon chain for lamellar MAPC in the interdigitated state. Furthermore, results suggest that free rotations of the glycerol C2-C3 bond within MAPC molecules may occur in the interdigitated bilayer, whereas intramolecular exchange between two conformations of the glycerol backbone in DPPC become possible at temperatures close to the pretransition temperature. Without isotope enrichment, we conclude that high-resolution solid-state 13C-NMR is indeed a useful technique which can be employed to study the packing and dynamics of phospholipids.
采用交叉极化/魔角旋转技术，在50.3 MHz下获得了单花生四烯酰磷脂酰胆碱（MAPC）和二棕榈酰磷脂酰胆碱（DPPC）分散体从25℃至55℃以及DPPC多晶体在25℃时的13C核磁共振谱。对DPPC和MAPC分散体的差示扫描量热研究表明，脂质相转变具有可比性，转变温度分别为41℃和45℃，因此能够比较这两个系统在相应温度下的热、结构和动力学差异。对DPPC分散体的构象依赖性13C化学位移研究不仅证明了波纹状凝胶（Pβ'）相中倾斜凝胶（Lβ'）和液晶（Lα）相的共存，还证明了存在中间的第三个微观相，这由ω-1亚甲基碳信号在Tp和Tm之间的温度区间出现三个可分辨峰所证明。通过比较MAPC在烃链区域的化学位移与DPPC在相似折合温度下的化学位移，可以得出结论，在层状向胶束转变过程中，脂肪酰链的中间段堆积受到显著扰动。然而，发现相互交错的MAPC片层的末端亚甲基和甲基比凝胶态下非相互交错的DPPC双层更有序。有趣的是，胶束中MAPC的末端甲基仍然相对有序；事实上，它们比液晶态下DPPC相应的酰链末端更有序。对旋转框架质子自旋晶格弛豫测量获得的数据进行分析表明，对于相互交错状态的层状MAPC，磷胆碱头部基团高度可移动，羰基刚性，烃链有序。此外，结果表明，MAPC分子内甘油C2-C3键的自由旋转可能发生在相互交错的双层中，而DPPC中甘油主链两种构象之间的分子内交换在接近预转变温度时变得可能。在没有同位素富集的情况下，我们得出结论, 高分辨率固态13C核磁共振确实是一种可用于研究磷脂堆积和动力学的有用技术。
