N-palmitoyl sphingomyelin bilayers: Structure and interactions with cholesterol and dipalmitoylphosphatidylcholine
N-palmitoyl sphingomyelin bilayers: Structure and interactions with cholesterol and dipalmitoylphosphatidylcholine
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DOI：
10.1021/bi9528356
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发表时间：
1996-06-18
期刊：
影响因子：
2.9
通讯作者：
Shipley, GG
中科院分区：
文献类型：
--
作者：
Maulik, PR;Shipley, GG
用差示扫描量热法(DSC)和X射线衍射法研究了N-棕榈酰鞘磷脂(C16：0-SM)的结构和热致性能及其与胆固醇和二棕榈酰磷脂酰胆碱(DPPC)的相互作用。C16：0-SM水合多层膜的DSC表现出可逆链熔化转变。在加热时，无水C16：0-SM在75℃(H=4.0千卡/摩尔)时发生吸热转变。逐渐增加水化会降低转变温度(T-M)并增加转变热(增量H)，直到观察到水化值的极限值(T-M=41℃，增量H=7.5千卡/摩尔)。在(29℃)T-M以下的X射线衍射表明，C16：0-SM在完全水化时为双层凝胶结构(d=73.5埃，锐化4.2埃反射)；高于T-M，在55℃时，存在双层液晶相(d=66.6埃，漫反射4.6埃)。在C16：0-SM双层膜中加入胆固醇后，在41℃时转变热逐渐降低，在>；50mol%胆固醇时没有检测到协同转变。X-射线衍射表明，当胆固醇的摩尔分数为50%时，在29℃和55℃时，两层膜的周期、广角反射的位置/宽度以及电子密度分布没有差别。因此，胆固醇插入到C16：0-SM双层分子中，逐渐消除了链熔化转变，改变了双层分子的结构特征。DSC和X-射线衍射数据表明，DPPC与C16：0-SM双层膜在凝胶相和液晶相都是完全相容的，但30mol%的C16：0-SM去除了DPPC的预相变。
The structure and thermotropic properties of N-palmitoyl sphingomyelin (C16:0-SM) and its interaction with cholesterol and dipalmitoylphosphatidylcholine (DPPC) have been studied by differential scanning calorimetry (DSC) and X-ray diffraction methods. DSC of hydrated multi-bilayers of C16:0-SM shows reversible chain-melting transitions. On heating, anhydrous C16:0-SM exhibits an endothermic transition at 75 degrees C (Delta H = 4.0 kcal/mol). Increasing hydration progressively lowers the transition temperature (T-M) and increases the transition enthalpy (Delta H), until limiting values (T-M = 41 degrees C, Delta H = 7.5 kcal/mol) are observed for hydration values >25 wt % H2O. X-ray diffraction at temperatures below (29 degrees C) T-M show a bilayer gel structure (d = 73.5 Angstrom, sharp 4.2 Angstrom reflection) for C16:0-SM at full hydration; above T-M, at 55 degrees C, a bilayer liquid-crystal phase is present (d = 66.6 Angstrom, diffuse 4.6 Angstrom reflection). Addition of cholesterol to C16:0-SM bilayers results in a progressive decrease in the enthalpy of the transition at 41 degrees C, and no cooperative transition is detected at >50 mol % cholesterol. X-ray diffraction shows no difference in the bilayer periodicity, position/width of the wide-angle reflections, or electron density profiles at 29 and 55 degrees C when 50 mol % cholesterol is present. Thus, cholesterol inserts into C16:0-SM bilayers progressively removing the chain-melting transition and changing the structural characteristics of the bilayer. DSC and X-ray diffraction data show that DPPC is completely miscible with C16:0-SM bilayers in both the gel and liquid-crystalline phases; however, 30 mol % C16:0-SM removes the pre-transition exhibited by DPPC.