Thermotropic behavior of glycosphingolipids in aqueous dispersions.
Thermotropic behavior of glycosphingolipids in aqueous dispersions.
复制标题
水分散体中鞘糖脂的热致行为。
作者：
Maggio,B;Ariga,T;Sturtevant,JM;Yu,RK
本文用高灵敏度差示扫描量热法研究了20种高纯度鞘糖脂（GSL）的热致性。一般来说，GSL的极性头基团似乎是其相行为的主要决定因素之一。与磷脂相比，极性头基中的碳水化合物而不是磷酸胆碱部分和GSL的烃部分中的鞘氨醇碱的存在降低了对由增加酰胺连接的脂肪酰基链中的亚甲基数目所带来的转变温度（Tm）的影响。对于简单的中性GSL，Tm比具有可比烃链的磷脂的Tm高20-40 ℃。随着GSL的寡糖链变得更加复杂，过渡的过量热容、Tm、焓（Δ fcal）和熵与极性头部基团中存在的碳水化合物残基的数量成比例地降低。阴离子GSL的Tm和Δ fcal比具有相当寡糖链的中性GSL的Tm和Δ fcal低16-25 ℃和1-3 kcal mol-1。但中性和阴离子GSL的斜率不同，表明两者的分子间结构不同。的Tm和/1的线性依赖于中性和阴离子GSL的分子面积，这表明在GSL的极性头基的复杂性的影响，建立热力学行为可能是介导的分子间间距。鞘脂（GSL）1是质膜的重要成分，并且在神经系统中特别丰富（Fishman和布雷迪，1976; Hakomori，1981; Leiden和Yu，1982; Leiden，1983; Ando，1983）。在髓磷脂中，糖脂（如半乳糖苷和硫苷脂）占总脂质的30%（Norton，1977）。神经系统膜也是独特的，其具有丰富的神经节苷脂，其是含有唾液酸的GSL（Hakomori，1981; Leiden & Yu，1982; Leiden，1983; Ando，1983）。在某些先天性代谢缺陷中，GSL的量异常增加（布雷迪，1982），而在一些神经系统疾病中，例如人类和实验性脱髓鞘疾病，GSL可以在质量或数量上选择性改变（Maggio等人，1972，1983; Yu等人，1974年，1982年）。GSL组成的这些改变总是导致不稳定的膜结构。此外，已经假定GSL在膜功能、细胞-细胞相互作用和细胞转化中起重要作用（Cumar等人，1970; Fishman &布雷迪，1976; Hakomori，1981）。它们也被假定为毒素、药物和天然激动剂的受体（Fishman和布雷迪，1976; Hakomori，1981; Leiden，1983; Ando，1983）。然而，这些脂质对细胞膜的结构和功能的影响的分子方面的任何理解仍然模糊。如果它们被认为是多分子动态系综的一部分，则情况更是如此，在多分子动态系综中，单个分子性质不再表现出，因为这些性质通过与其他脂质和蛋白质的分子间相互作用而改变（Maggio等人，1981年）。系统研究了几种化学相关的GSL与天然和合成磷脂以及与f建立的各个界面性质和相互作用，得到了美国国立卫生研究院（National Institutes of Health）赠款NS-11853和GM-04725、美国国家科学基金会（National Science Foundation）赠款PCM-8117341和美国国家科学基金会（National Science Foundation）的资助。
The thermotropic behavior of 20 chemically related glycosphingolipids (GSLs) of high purity, containing neutral and anionic carbohydrate residues in their oligosaccharidechains, was studied by high-sensitivity differential scanning calorimetry. In general, the polar head group of GSLs appears to be one of the major determinants of their phase behavior. Compared to phospholipids, the presence of the carbohydrate rather than the phosphorylcholine moiety in the polar head group and a sphingosine base in the hydrocarbon portion of GSLs reduces the effect on the transition temperature (Tm) brought about by increasing the number of methylene groups in the amide-linked fatty acyl chains. For simple neutral GSLs, the Tm’s were 20-40 C higher than those of phospholipids with comparable hydrocarbon chains. As the oligosaccharide chain of GSLs becomes more complex, the excess heat capacity, Tm, enthalpy (A£ fcal), and entropy of the transition decrease proportionally to the number of carbohydrate residues present in the polar head group. The Tm and A£ fcal for anionic GSLs were 16-25 C and 1-3 kcal mol™ 1 lower than those of neutral GSLs with comparable oligosaccharide chains. A linear dependence of/^ with Tm was found. However, the slopes of these plots were different for neutral and for anionic GSLs, suggesting different types of intermolecularorganizations for the two. The Tm and/1 were linearly dependent on the molecular area of both neutral and anionic GSLs; this indicated that the influence of the complexity of the polar head group in GSLs for establishing the thermodynamic behavior may be mediated by the intermolecular spacings.(jllycosphingolipids (GSLs) 1 are important constituents of plasma membranes and are particularly abundant in the nervous system (Fishman & Brady, 1976; Hakomori, 1981; Ledeen & Yu, 1982; Ledeen, 1983; Ando, 1983). In myelin, glycolipids such as galactocerebrosides and sulfatides account for 30% of total lipids (Norton, 1977). The nervous system membranes are also unique in having an abundance of gangliosides which are sialic acid containing GSLs (Hakomori, 1981; Ledeen & Yu, 1982; Ledeen, 1983; Ando, 1983). In certain inborn errors of metabolism, the amount of GSLs is abnormally increased (Brady, 1982) whereas in some neuro-logical disorders, such as human and experimental demyelinating diseases, the GSLs can be selectively altered in quality or quantity (Maggio et al., 1972, 1983; Yu et al., 1974, 1982). These alterations in the composition of GSLs invariably lead to an unstable membrane structure. In addition, GSLs have been postulated to play an important role in membrane function, cell-cell interaction, and cell transformation (Cumar et al., 1970; Fishman & Brady, 1976; Hakomori, 1981). They have also been postulated to serve as receptors for toxins, drugs, and natural agonists (Fishman & Brady, 1976; Hakomori, 1981; Ledeen, 1983; Ando, 1983). However, any understanding in molecular terms of the effects of these lipids on the structure and function of cell membranes remains obscure. This is even more so if they are considered as part of multi-molecular dynamic ensembles in which the individual mo-lecular properties are no longer exhibited as these properties become modified by intermolecular interactions with other lipids and proteins (Maggio et al., 1981). Systematic studies of the individual interfacial properties and interactions that several chemically related GSLs can establish with natural and synthetic phospholipids and with f Supported by National Institutes of Health Grants NS-11853 and GM-04725, National Science FoundationGrant PCM-8117341, and National …