多烯脂肪酸对磷脂胆固醇液晶态结构影响机理

用小角Ｘ 射线散射法、３１Ｐ 核磁共振技术和扫描隧道显微镜技术,对多烯脂肪酸多相脂质体的液晶态结构进行了研究。实验结果表明：胆固醇、多烯脂肪酸、非离子表面活性剂均对ＰＥ 脂质体的液晶态结构有明显的影响。在含有高效分散剂的磷酸缓冲溶液中制成的液晶态油酸多相脂质体和亚油酸多相脂质体均由片层六角相和片层立方相组成, 而蓖麻酸多相脂质体由立方六角相组成。     

同脂膜结合的短杆菌肽S的扫描隧道显微镜观察

将短杆菌肽Ｓ与二棕榈酰磷脂酰胆碱脂质体复合物滴于高定向裂解石墨,充分干燥后,用扫描隧道显微镜进行观察,可以得到：１．磷脂分子在石墨表面有规则的二维排列的图像;２．短杆菌肽Ｓ在石墨表面自组合形成的二维晶体的图像和３．短杆菌肽Ｓ平躺于磷脂分子头部的图像。根据短杆菌肽Ｓ在石墨上排列的二维晶格常数和分子大小可知,在石墨表面,短杆菌肽Ｓ以二聚体形式存在。这同短杆菌肽Ｓ的晶体衍射结果一致。但从短杆菌肽Ｓ平躺于磷脂头部的图像上可以分辨出：在脂环境中,短杆菌肽Ｓ以单体形式存在。最后,根据短杆菌肽Ｓ分子的大小与磷脂分子在石墨表面排列的二维晶格常数,得出了短杆菌肽Ｓ同二棕榈酰磷脂酰胆碱分子的作用模式图     

苯及丙酮对磷酯酰乙醇胺液晶态结构的影响

用小角Ｘ射线散射研究了苯、丙酮对磷脂酰乙醇胺液晶态结构的影响,实验结果表明,苯能命名ＰＥ液晶态先从片层相解束变成立方相,然后再诱导立方相变成六角形ＨⅡ相,最后促使六角形ＨⅡ相解束变成液态,束相变中出现了红移现象,丙酮也有使ＰＥ液晶态先从片层相解束变成立方相,在解束相变中也出现红移现象,但再诱导立方相变成六角形ＨⅡ相之后,不是促使其变成液相,而是将其稳定在六角形ＨⅡ相。     

苯及丙酮对磷脂酰乙醇胺液晶态结构的影响

用小角 X 射线散射(SAXS)法研究了苯、丙酮对磷脂酰乙醇胺(PE)液晶态结构的影响.实验结果表明:苯能使 PE 液晶态先从片层相解束变成立方相.然后再诱导立方相变成六角形 H_Ⅱ相,最后促使六角形 H_Ⅱ相解束变成液态.在解束相变中出现了红移现象.丙酮也有使 PE 液晶态先从片层相解束变成立方相,在解束相变中也出现红移现象,但再诱导立方相变成六角形 H_Ⅱ相之后,不是促使其变成液相,而是将其稳定在六角形 H_Ⅱ相.     

DMPC单分子层膜及细胞色素C氧化酶重组脂质体表面的扫描隧道显微镜观察

本文报导了扫描隧道显微镜对固相磷脂单分子层膜以及重组了细胞色素C氧化酶后的脂质体表面结构的观察.对DMPC单分子层著,得到了有关磷脂头部形态,大小及排态状况等结构信息,达到分子水平分辨;对重组酶后的脂质体表面,也得到了氧化酶分子在膜上的结构信息.     

DMPC单分子层膜及细胞色素C氧化酶重组脂质体表面的扫描隧道显微镜观察

本文报导了扫描隧道显微镜对固相磷脂单分子层膜以及重组了细胞色素C氧化酶后的脂质体表面结构的观察.对DMPC单分子层著,得到了有关磷脂头部形态,大小及排态状况等结构信息,达到分子水平分辨;对重组酶后的脂质体表面,也得到了氧化酶分子在膜上的结构信息.     

脂质体研究及其应用前景

前言早在60年代初,Bangham等就已发现双亲性分子(一端亲水、另一端疏水的分子)在水中将自动形成多层的封闭囊泡,其中每一层都由亲水端朝向水、疏水端彼此靠近、排列有序的二片层分子组成。他把这种结构称为片层液晶相。磷脂就是这种双亲性分子的典型代表,用磷脂充分水化后所形成的上述结构在许多方面类似于生物膜,是在分子水平研究膜结构与功能的很好的模型,因此有关这类研究工作就迅速发展起来。Sessa与Weissman于1968年正式提出脂质体这一名词,并为各国学者所公认和广为采用。虽然脂质体可能具有不同的形式,例如柱形甚至螺旋形的结构,但多数情况下以近似圆     

磷脂DMPC Langmuir－Blodgett膜晶格结构的原子力显微镜研究

用原子力显微镜（ＡＦＭ）研究了磷脂ＤＭＰＣ三层Ｌａｎｇｍｕｉｒ－Ｂｌｏｄｇｅｔｔ（ＬＢ）膜的分子排列结构,结果表明：在磷脂ＬＢ膜的两相（液体压缩相Ｌｉｑｕｉｄ－ｃｏｎｄｅｎｓｅｄｐｈａｓｅ和液体扩张相Ｌｉｑｕｉｄ－ｅｘｐａｎｄｅｄｐｈａｓｅ）共存时,液体压缩相中的磷脂分子排列紧密,取向一致,分子间作用力较大,因而能够得到分子图像。而液体扩张相中的磷脂分子排列松散,取向混乱。分子间的作用力较弱,难于得到分子图像。在液体压缩相中磷脂分子以单斜晶格结构排列,分子间隔为０．７２ｎｍ．分子高度为２．１ｎｍ。这一结果和ＤＭＰＣ的单晶结构进行了比较。     

磷脂DMPC Langmuir－Blodgett膜晶格结构的原子力显微镜研究

用原子力显微镜（ＡＦＭ）研究了磷脂ＤＭＰＣ三层Ｌａｎｇｍｕｉｒ－Ｂｌｏｄｇｅｔｔ（ＬＢ）膜的分子排列结构,结果表明：在磷脂ＬＢ膜的两相（液体压缩相Ｌｉｑｕｉｄ－ｃｏｎｄｅｎｓｅｄｐｈａｓｅ和液体扩张相Ｌｉｑｕｉｄ－ｅｘｐａｎｄｅｄｐｈａｓｅ）共存时,液体压缩相中的磷脂分子排列紧密,取向一致,分子间作用力较大,因而能够得到分子图像。而液体扩张相中的磷脂分子排列松散,取向混乱。分子间的作用力较弱,难于得到分子图像。在液体压缩相中磷脂分子以单斜晶格结构排列,分子间隔为０．７２ｎｍ．分子高度为２．１ｎｍ。这一结果和ＤＭＰＣ的单晶结构进行了比较。     

免疫球蛋白G(IgG)分子结构的扫描隧道显微镜观察

把溶于双蒸水的兔IgG铺展在高定向石墨(HOPG)底载上,直接用扫描隧道显微镜(Scanning Tunneling Microscopy,简称STM)在大气环境中观察,得到了IgG分子的表面结构图像。从图像上可清晰地分辨出IgG分子的Fab及Fc片段,片段连接处的"铰链区"以及Fab和F_e片段的某些精细结构(IgG分子功能辖区)。本工作表明STM在研究生物大分子天然结构方面有巨大潜力。     

Phase separations of alpha-tocopherol in aqueous dispersions of distearoylphosphatidylethanolamine

The effect of alpha-tocopherol on the structure and thermotropic phase behaviour of distearoylphosphatidylethanolamine was examined by using synchrotron X-ray diffraction methods. There was evidence that alpha-tocopherol does not distribute randomly in the dispersed phospholipid but instead phospholipid phases enriched in alpha-tocopherol are formed. Heating codispersions from lamellar gel phase induced formation of hexagonal-II phase at temperatures below the main transition of the pure phospholipid and which were enriched in alpha-tocopherol. Codispersions containing 5 or 10 mol% alpha-tocopherol were induced to form a cubic phase at temperatures above the lamellar to hexagonal-II phase transition. Such phases were not observed in codispersions containing 2.5 or 20 mol% alpha-tocopherol in which only lamellar and hexagonal-II phases were formed. The space group of the cubic phases were tentatively assigned as Pn3m. Equilibration of codispersions at 4 degrees C results in the formation of lamellar crystalline phases enriched in alpha-tocopherol and phase separated domains of pure phospholipid. Two lamellar crystalline phases were characterized on the basis of their particular wide-angle X-ray scattering patterns. The lamellar crystalline phases were also distinguished from other lamellar phases of the pure phospholipid by the lamellar repeat. Partitioning of alpha-tocopherol into phosphatidylethanolamine domains in membranes may introduce instability into the structure.     

Effects of diacylglycerol on the structure and phase behaviour of non-bilayer forming phospholipid

The phase behaviour of mixed aqueous dispersions of the monomethyl derivative of dioleoylphosphatidylethanolamine and dipalmitoylglycerol has been characterised by X-ray diffraction, differential scanning calorimetry and freeze-fracture electron microscopy for mixtures containing dipalmitoylglycerol in the concentration range 0-20 mol%. Dispersions prepared at temperatures where the phospholipid exhibits a liquid-crystalline lamellar phase show that dipalmitoylglycerol is completely phase separated into aggregates of stable crystal phase (beta'-phase). Heating mixed dispersions results in transformation of lamellar into hexagonal-II structure commencing at approximately 45 degrees C. This temperature coincides with a disappearance of beta'-phase of DPG which becomes incorporated into hexagonal-II phase. The pure phospholipid is transformed upon cooling from hexagonal-II into characteristic cubic phases; the formation of cubic phase is prevented by the presence of dipalmitoylglycerol and mixed dispersions initially form a lamellar liquid-crystalline phase in which the lipids are phase separated. The X-ray and thermal data suggest that relatively small domains of metastable crystal phase (alpha-phase) of DPG form initially on cooling and these subsequently coalesce and transform to beta'-phase.     

Inverted hexagonal and cubic phases induced by alpha-tocopherol in fully hydrated dispersions of dilauroylphosphatidylethanolamine

The effect of alpha-tocopherol on the thermotropic phase behaviour and structure of aqueous dispersions of 1,2-di-lauryl-sn-glycero-3-phosphoethanolamine was examined by synchrotron X-ray diffraction. The pure phospholipid exhibited a lamellar gel to liquid-crystal phase transition at 30 degrees C on heating at 3 degrees C min(-1) between 10 degrees C and 90 degrees C. The transition was reversible with a temperature hysteresis of 0.3 degrees C on cooling. At temperatures less than 10 degrees C only lamellar gel phase of the pure phospholipid was seen in co-dispersions of up to 20 mol % alpha-tocopherol. The presence of 2.5 mol % alpha-tocopherol caused the appearance of inverted hexagonal phase at temperatures just below the main phase transition temperature that co-existed with the lamellar gel phase. The intensity of scattering from the hexagonal-II phase increased with increasing proportion of alpha-tocopherol in the mixture and in proportions greater than 10 mol % it persisted at temperatures above the main transition and co-existed with the lamellar liquid-crystal phase of the pure phospholipid. At higher temperatures all co-dispersions containing up to 15 mol % alpha-tocopherol showed the presence of cubic phases. These phases indexed a Pn3m or Pn3 space grouping. When the proportion of alpha-tocopherol was increased to 20 mol % the only non-lamellar phase observed was inverted hexagonal phase. This phase co-existed with lamellar gel and liquid-crystal phases of the pure phospholipid, but was the only phase present at temperatures >60 degrees C. The X-ray diffraction data were used to construct a partial phase diagram of the lipid mixture in excess water between 10 degrees and 90 degrees C and up to 20 mol % alpha-tocopherol in phospholipid.     

Cubic phase is induced by cholesterol in the dispersion of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine

The effect of cholesterol, a major constituent of eukaryotic cell membranes, on the structure and thermotropic phase behaviour of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) dispersed in excess water was examined by synchrotron X-ray diffraction methods. Temperature scans over the range 10-75 degrees C showed that the gel to liquid-crystalline phase transition decreased from 25 to 10 degrees C in the presence of 20 mol% cholesterol, and no gel phase could be detected in the wide-angle X-ray scattering (WAXS) intensity profile of mixtures containing 35 mol% cholesterol. The small-angle X-ray scattering (SAXS) intensity profiles showed that the lamellar to nonlamellar phase transition temperature was also decreased in mixtures containing up to 30 mol% cholesterol but the trend was reversed in mixtures containing a higher proportion of cholesterol. There was evidence that the transition of the lamellar liquid-crystal phase is to cubic phases in mixtures containing less than 30 mol% cholesterol. The space group of one of these cubic phases was assigned as Pn3m. This effect of cholesterol on non-bilayer-forming phospholipids is considered in the context of the role of cholesterol in membrane organization and function.     

An X-ray diffraction study of the effect of alpha-tocopherol on the structure and phase behaviour of bilayers of dimyristoylphosphatidylethanolamine.

The effect of alpha-tocopherol on the thermotropic phase transition behaviour of aqueous dispersions of dimyristoylphosphatidylethanolamine was examined using synchrotron X-ray diffraction methods. The temperature of gel to liquid-crystalline (Lbeta-->Lalpha) phase transition decreases from 49.5 to 44.5 degrees C and temperature range where gel and liquid-crystalline phases coexist increases from 4 to 8 degrees C with increasing concentration of alpha-tocopherol up to 20 mol%. Codispersion of dimyristoylphosphatidylethanolamine containing 2.5 mol% alpha-tocopherol gives similar lamellar diffraction patterns as those of the pure phospholipid both in heating and cooling scans. With 5 mol% alpha-tocopherol in the phospholipid, however, an inverted hexagonal phase is induced which coexists with the lamellar gel phase at temperatures just before transition to liquid-crystalline lamellar phase. The presence of 10 mol% alpha-tocopherol shows a more pronounced inverted hexagonal phase in the lamellar gel phase but, in addition, another non-lamellar phase appears with the lamellar liquid-crystalline phase at higher temperature. This non-lamellar phase coexists with the lamellar liquid-crystalline phase of the pure phospholipid and can be indexed by six diffraction orders to a cubic phase of Pn3m or Pn3 space groups and with a lattice constant of 12.52+/-0.01 nm at 84 degrees C. In mixed aqueous dispersions containing 20 mol% alpha-tocopherol, only inverted hexagonal phase and lamellar phase were observed. The only change seen in the wide-angle scattering region was a transition from sharp symmetrical diffraction peak at 0.43 nm, typical of gel phases, to broad peaks centred at 0.47 nm signifying disordered hydrocarbon chains in all the mixtures examined. Electron density calculations through the lamellar repeat of the gel phase using six orders of reflection indicated no difference in bilayer thickness due to the presence of 10 mol% alpha-tocopherol. The results were interpreted to indicate that alpha-tocopherol is not randomly distributed throughout the phospholipid molecules oriented in bilayer configuration, but it exists either as domains coexisting with gel phase bilayers of pure phospholipid at temperatures lower than Tm or, at higher temperatures, as inverted hexagonal phase consisting of a defined stoichiometry of phospholipid and alpha-tocopherol molecules.     

X-ray diffraction study of feline leukemia virus fusion peptide and lipid polymorphism

The structural effects of the fusion peptide of feline leukemia virus (FeLV) on the lipid polymorphism of N-methylated dioleoylphosphatidylethanolamine were studied using a temperature ramp with sequential X-ray diffraction. This peptide, the hydrophobic amino-terminus of p15E, has been proven to be fusogenic and to promote the formation of highly curved, intermediate structures on the lamellar liquid-crystal to inverse hexagonal phase transition pathway. The FeLV peptide produces marked effects on the thermotropic mesomorphic behaviour of MeDOPE, a phospholipid with an intermediate spontaneous radius of curvature. The peptide is shown to reduce the lamellar repeat distance of the membrane prior to the onset of an inverted cubic phase. This suggests that membrane thinning may play a role in peptide-induced membrane fusion and strengthens the link between the fusion pathway and inverted cubic phase formation. The results of this study are interpreted in relation to models of the membrane fusion mechanism.     

The kinetics and mechanism of the formation of crystalline phase of dipalmitoylphosphatidylethanolamine dispersed in aqueous dimethyl sulfoxide solutions

The phase transition kinetics and mechanism of formation of a lamellar-crystalline phase of dipalmitoylphosphatidylethanolamine (DPPE) dispersed in different concentrations of aqueous dimethyl sulfoxide (DMSO) during cooling have been examined by differential scanning calorimetry and synchrotron X-ray diffraction techniques. In dispersions containing mole fractions of DMSO (x<0.22), the phase transition sequence of the phospholipid is from lamellar liquid-crystal phase to lamellar-gel phase. Increasing the mole fraction of DMSO to 0.220.5 resulted in a direct transition from liquid-crystal phase to lamellar crystal phase with no detectable intermediate gel phase. A temperature versus DMSO concentration phase diagram was constructed based on calorimetric data with phase assignments made using synchrotron X-ray diffraction measurements. The non-isothermal formation kinetics of the lamellar crystal phase, which is expressed as the half time of the transformation process, was found to depend on DMSO concentration. The inducement of lamellar crystal phase in DPPE by DMSO is discussed in terms of the dehydration effect of DMSO and competitive molecular interactions between DMSO, water, and the phospholipid.     

The interaction of coenzyme Q with phosphatidylethanolamine membranes.

Coenzyme Q (CoQ) is a component of the mitochondrial respiratory chain which carries out additional membrane functions, such as acting as an antioxidant. The location of CoQ in the membrane and the interaction with the phospholipid bilayer is still a subject of debate. The interaction of CoQ in the oxidized (ubiquinone-10) and reduced (ubiquinol-10) state with membrane model systems of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (Ela2Gro-P-Etn) has been studied by means of differential scanning calorimetry (DSC), 31P-nuclear magnetic resonance (31P-NMR) and small angle X-ray diffraction (SAXD). Ubiquinone-10 did not visibly affect the lamellar gel to lamellar liquid-crystalline phase transition of Ela2Gro-P-Etn, but it clearly perturbed the multicomponent lamellar liquid-crystalline to lamellar gel phase transition of the phospholipid. The perturbation of both transitions was more effective in the presence of ubiquinol-10. A location of CoQ forming head to head aggregates in the center of the Ela2Gro-P-Etn bilayer with the polar rings protruding toward the phospholipid acyl chains is suggested. The formation of such aggregates are compatible with the strong hexagonal HII phase promotion ability found for CoQ. This ability was evidenced by the shifting of the lamellar to hexagonal HII phase transition to lower temperatures and by the appearance of the characteristic hexagonal HII 31P-NMR resonance and SAXD pattern at temperatures at which the pure Ela2Gro-P-Etn is still organized in extended bilayer structures. The influence of CoQ on the thermotropic properties and phase behavior of Ela2Gro-P-Etn is discussed in relation to the role of CoQ in the membrane.     

Cubic phase is induced by cholesterol in the dispersion of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine

The effect of cholesterol, a major constituent of eukaryotic cell membranes, on the structure and thermotropic phase behaviour of 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) dispersed in excess water was examined by synchrotron X-ray diffraction methods. Temperature scans over the range 10-75 °C showed that the gel to liquid-crystalline phase transition decreased from 25 to 10 °C in the presence of 20 mol% cholesterol, and no gel phase could be detected in the wide-angle X-ray scattering (WAXS) intensity profile of mixtures containing 35 mol% cholesterol. The small-angle X-ray scattering (SAXS) intensity profiles showed that the lamellar to nonlamellar phase transition temperature was also decreased in mixtures containing up to 30 mol% cholesterol but the trend was reversed in mixtures containing a higher proportion of cholesterol. There was evidence that the transition of the lamellar liquid-crystal phase is to cubic phases in mixtures containing less than 30 mol% cholesterol. The space group of one of these cubic phases was assigned as Pn3m. This effect of cholesterol on non-bilayer-forming phospholipids is considered in the context of the role of cholesterol in membrane organization and function.     

Stabilization of non-bilayer structures by the etherlipid ethanolamine plasmalogen

The thermotropic phase behavior of mixtures between diradylphosphatidylethanolamines and diacylphosphatidylcholine was studied using polarized light microscopy, 31P-NMR spectroscopy and synchrotron X-ray diffraction. Multilamellar liposomes composed of alkenylacylphosphatidylethanolamine (ethanolamine plasmalogen) undergo a phase transition from a lamellar to an inverse hexagonal lipid structure at 30 degrees C, which is about 20 degrees C and 30 degrees C lower as compared to its alkylacyl- and diacyl-analog, respectively. These results indicate a higher affinity to non-bilayer structures for the ether lipids. In the presence of the bilayer stabilizing phospholipid, palmitoyloleoylphosphatidylcholine, the transition is shifted to higher temperature without any significant changes in the overall structural parameters as revealed by X-ray diffraction experiments. Again, ethanolamine plasmalogen stabilizes the inverted hexagonal phase to the highest extent, i.e. even in the presence of 40 mol% palmitoyloleoylphosphatidylcholine a pure inverse hexagonal phase is formed at 60 degrees C. Such a result was not reported so far for a diacylphosphatidylethanolamine. This property of ethanolamine plasmalogen might be predominantly explained by an optimized packing of the hydrocarbon chains in the corners and interface region of the hexagonal tubes, owing to a different conformation of the sn-2 chain, which was deduced from 2H-NMR experiments (Malthaner, M., Hermetter, A., Paltauf, F. and Seelig, J. (1987) Biochim. Biophys. Acta 900, 191-197). Data obtained by time resolved X-ray diffraction show a coexistence of lamellar and inverse hexagonal structures in the phase transition region, but do not indicate the existence of non-lamellar intermediates or disorder within the sensitivity limits of the method.