Brandenburg K, Funari S S, Koch M H, Seydel U
Center for Medicine and Biosciences, Research Center Borstel, Borstel, D-23845, Germany.
J Struct Biol. 1999 Dec 15;128(2):175-86. doi: 10.1006/jsbi.1999.4186.
The acyl chain packing of various endotoxins and phospholipids was monitored via the main wide-angle reflection between 0.410 and 0.460 nm by wide-angle X-ray scattering (WAXS) and via the absorption band of the symmetric stretching vibration of the methylene groups v(s)(CH(2)) around 2849 to 2853 cm(-1) by Fourier-transform infrared spectroscopy. The lipids investigated included various rough mutant (R) and smooth form (S) lipopolysaccharides (LPS) differing in the length of the sugar portion, lipid A, the "endotoxic principle" of LPS, and various saturated and unsaturated phospholipids with different head groups under a near physiological (>/=85%) water content. The packing density of the saturated endotoxin acyl chains is lower than those of saturated phospholipids but similar to those of monounsaturated phospholipids, each in the gel phase. The hydrophobic moiety of endotoxins thus exhibits significant conformational disorder already in the gel phase. The acyl chain packing of the endotoxins decreases with increasing length of the sugar chain lengths, which seems to be relevant to the observed differences in biological activity. For Re-LPS with different counterions (salt forms), in the presence of externally added cations or at reduced water content (50%), no change of the acyl chain packing density is deduced in the X-ray data, although the FT-IR data indicate its increase. The position of the v(s)(CH(2)) vibration is, thus, only a relative measure of lipid order, in particular when lipids with different head groups and in the presence of external agents are compared.
通过广角X射线散射（WAXS）监测0.410至0.460 nm之间的主要广角反射，以及通过傅里叶变换红外光谱监测亚甲基对称伸缩振动v(s)(CH(2))在2849至2853 cm(-1)附近的吸收带，来监测各种内毒素和磷脂的酰基链堆积情况。所研究的脂质包括各种糖部分长度不同的粗糙突变型（R）和平滑型（S）脂多糖（LPS）、脂质A（LPS的“内毒素原理”），以及在接近生理（≥85%）水含量下具有不同头部基团的各种饱和和不饱和磷脂。饱和内毒素酰基链的堆积密度低于饱和磷脂，但与单不饱和磷脂在凝胶相中的堆积密度相似。因此，内毒素的疏水部分在凝胶相中就已经表现出显著的构象无序。内毒素的酰基链堆积随着糖链长度的增加而降低，这似乎与观察到的生物活性差异有关。对于具有不同抗衡离子（盐形式）的Re-LPS，在外部添加阳离子或水含量降低（50%）的情况下，X射线数据推断酰基链堆积密度没有变化，尽管傅里叶变换红外光谱数据表明其增加。因此，v(s)(CH(2))振动的位置只是脂质有序性的相对度量，特别是在比较具有不同头部基团的脂质以及存在外部试剂的情况下。
