Lotta T I, Salonen I S, Virtanen J A, Eklund K K, Kinnunen P K
Department of Membrane Physics, KSV Research Laboratories, Helsinki, Finland.
Biochemistry. 1988 Oct 18;27(21):8158-69. doi: 10.1021/bi00421a026.
Molecular packing and the thermotropic phase behavior of fully hydrated ammonium salts of 1,2-dimyristoyl-sn-glycero-3-phosphatidyl-sn-1'-glycerol (1'-DMPG) and the corresponding 3' stereoisomer (3'-DMPG) as well as the effects of 300 mM NaCl on these lipids were studied by Fourier transform infrared (FTIR) spectroscopy. The ammonium salts of both stereoisomer show similar thermotropic phase behavior and have an order-disorder phase transition at approximately 21 degrees C. While complexing with Na+, however, an incubation of liposomes at +6 degrees C for 3 days results in significant structural differences between liposomes of 1'-DMPG and 3'-DMPG. In the presence of 300 mM NaCl the infrared spectra for 3'-DMPG reveal the appearance of a more solidified lipid nominated here as the highly crystalline phase with a transition into the liquid-crystalline state at a significantly higher temperature (approximately at 33 degrees C) than that for 1'-DMPG (approximately at 23 degrees C). Crystal field splitting resulting from interchain vibrational coupling is observed in the CH2 scissoring mode of the 3'-DMPG(Na+) complex in the highly crystalline phase (T less than 33 degrees C); i.e., the acyl chains are packed in a rigid orthorhombic- or monoclinic-like crystal lattice. At temperatures above the transition at 33 degrees C the acyl chains of 3'-DMPG(Na+) give rise to infrared spectra indicative of hexagonal packing. The latter type of hydrocarbon chain packing is also found for the ammonium salts of 1'-DMPG and 3'-DMPG without Na+ as well as for 1'-DMPG with Na+. In addition, the binding of Na+ to 3'-DMPG causes narrowing of the bands associated with the interfacial and polar headgroup regions of 3'-DMPG and thus reveals reduced motional freedom. This demonstrates that Na+ binds tightly to 3'-DMPG, leading to the immobilization of the entire phospholipid polar headgroup. Such effects by Na+ are not observed for 1'-DMPG.
采用傅里叶变换红外光谱法（FTIR）研究了1,2 - 二肉豆蔻酰 - sn - 甘油 - 3 - 磷脂酰 - sn - 1'-甘油（1'-DMPG）及其相应的3'立体异构体（3'-DMPG）的完全水合铵盐的分子堆积和热致相行为，以及300 mM NaCl对这些脂质的影响。两种立体异构体的铵盐表现出相似的热致相行为，在约21℃有有序 - 无序相变。然而，与Na +络合时，脂质体在+6℃孵育3天导致1'-DMPG和3'-DMPG脂质体之间存在显著的结构差异。在300 mM NaCl存在下，3'-DMPG的红外光谱显示出现一种更固化的脂质，在此命名为高度结晶相，其转变为液晶态的温度（约33℃）明显高于1'-DMPG（约23℃）。在高度结晶相（T小于33℃）的3'-DMPG（Na +）络合物的CH2剪式振动模式中观察到由链间振动耦合引起的晶体场分裂；即，酰基链以刚性正交或单斜晶系晶格堆积。在高于33℃转变温度时，3'-DMPG（Na +）的酰基链产生表明六方堆积的红外光谱。对于没有Na +的1'-DMPG和3'-DMPG的铵盐以及含有Na +的1'-DMPG也发现了后一种类型的烃链堆积。此外，Na +与3'-DMPG的结合导致与3'-DMPG的界面和极性头部区域相关的谱带变窄，从而显示出运动自由度降低。这表明Na +与3'-DMPG紧密结合，导致整个磷脂极性头部固定。对于1'-DMPG未观察到Na +的这种作用。
