Boggs J M, Mulholland D, Koshy K M
Department of Biochemistry, Hospital for Sick Children, Toronto, Ont., Canada.
Biochem Cell Biol. 1990 Jan;68(1):70-82. doi: 10.1139/o90-009.
The phase behavior of mixtures of dipalmitoyl phosphatidylcholine (DPPC) with semisynthetic species of cerebroside sulfate (CBS) containing palmitic acid (C16:0-CBS) or lignoceric acid (C24:0-CBS) in 0.1 M KCl was studied using differential scanning calorimetry. DPPC and C16:0-CBS were miscible in all proportions in the gel phase above 10 mol% CBS and in the liquid-crystalline phase. However, C24:0-CBS was less miscible with DPPC over a wide concentration range in the gel phase. At high CBS concentrations it was probably also not entirely miscible with DPPC in the liquid-crystalline phase. Small amounts of both species of CBS lowered the transition temperature and enthalpy of DPPC, suggesting that they are more soluble in the liquid-crystalline phase of DPPC than the gel phase. The transition temperature at higher CBS concentrations was also less than expected, especially after cycling through the phase transition in the case of C24:0-CBS, suggesting that mixing with DPPC inhibited the intermolecular hydrogen bonding interactions and dehydration of CBS. In C24:0-CBS-DPPC mixtures several populations were present over a wide compositional range, including two solid-solid solutions of fixed composition. At high C24:0-CBS concentrations some C24:0-CBS also phase separated out of the mixture. Structural considerations suggested that the C24:0-CBS which is mixed with DPPC must be interdigitated into the DPPC bilayer. Other populations that are present may have a different structural organization. A fatty acid spin label in these mixtures was a little less ordered than in either lipid by itself. The permeability of these lipids, as well as the two asymmetric species 1-stearoyl-2-caproyl phosphatidylcholine and 1-stearoyl-2-myristoyl phosphatidylcholine (18:10PC and 18:14PC), to a water-soluble spin label tempocholine chloride was also measured. The studies with 18:10PC and 18:14PC indicated that both triple-chain mixed interdigitated bilayers and double-chain partially interdigitated bilayers can trap water-soluble substances and have low permeability. Both species of CBS could also entrap the spin label and had low permeability at 4 degrees C. However, they rapidly lost the entrapped compound when they transformed into their stable dehydrated phases or into the liquid-crystalline phase. Mixing with DPPC prevented both of these losses. These studies supported the conclusion that a significant amount of the CBS was mixed with the DPPC and that this mixing prevented the dehydration changes which CBS undergoes by itself.(ABSTRACT TRUNCATED AT 400 WORDS)
使用差示扫描量热法研究了二棕榈酰磷脂酰胆碱（DPPC）与含有棕榈酸（C16:0-CBS）或木蜡酸（C24:0-CBS）的半合成硫酸脑苷脂（CBS）混合物在0.1 M KCl中的相行为。在CBS含量高于10 mol%时，DPPC和C16:0-CBS在凝胶相和液晶相中均能以任意比例互溶。然而，在凝胶相中，C24:0-CBS在较宽的浓度范围内与DPPC的互溶性较差。在高CBS浓度下，它在液晶相中可能也不能完全与DPPC互溶。两种CBS都能少量降低DPPC的转变温度和焓，这表明它们在DPPC的液晶相中的溶解度高于凝胶相。在较高CBS浓度下的转变温度也低于预期，尤其是在C24:0-CBS经历相变循环后，这表明与DPPC混合会抑制CBS的分子间氢键相互作用和脱水。在C24:0-CBS-DPPC混合物中，在较宽的组成范围内存在多个组分，包括两种固定组成的固-固溶液。在高C24:0-CBS浓度下，一些C24:0-CBS也会从混合物中相分离出来。结构分析表明与DPPC混合的C24:0-CBS必须插入到DPPC双层中。其他存在的组分可能具有不同的结构组织。这些混合物中的脂肪酸自旋标记的有序度比单独的任何一种脂质都略低。还测量了这些脂质以及两种不对称脂质1-硬脂酰-2-己酰磷脂酰胆碱和1-硬脂酰-2-肉豆蔻酰磷脂酰胆碱（18:10PC和18:14PC）对水溶性自旋标记氯化tempocholine的通透性。对18:10PC和18:14PC的研究表明，三链混合交错双层和双链部分交错双层都能捕获水溶性物质且通透性较低。两种CBS也能捕获自旋标记，并且在4℃时通透性较低。然而，当它们转变为稳定的脱水相或液晶相时，会迅速失去捕获的化合物。与DPPC混合可防止这两种损失。这些研究支持了以下结论：大量的CBS与DPPC混合，并且这种混合阻止了CBS自身发生的脱水变化。（摘要截断于400字）
