Polymorphism of a lipid extract from Pseudomonas fluorescens: structure analysis of a hexagonal phase and of a novel cubic phase of extinction symbol Fd--.
Polymorphism of a lipid extract from Pseudomonas fluorescens: structure analysis of a hexagonal phase and of a novel cubic phase of extinction symbol Fd--.
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荧光假单胞菌脂质提取物的多态性：六方相和消光符号 Fd-- 的新型立方相的结构分析。
DOI：
10.1021/bi00481a007
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发表时间：
1990
期刊：
影响因子：
2.9
通讯作者：
Herve Delacroix
中科院分区：
文献类型：
--
作者：
Paolo Mariani;Emilio Rivas;Vittorio Luzzati;Herve Delacroix
荧光假单胞菌脂肪提取物的相图是不寻常的，因为它显示出由六方相跨越的立方相。在一个扩展的浓度范围内研究了六方相，并且在假定该结构包含已知半径的圆柱体的情况下对反射进行了相移。用227号空间群(Fd3m)分析了消光符号为fd--的立方相。通过使用一种新的模式识别方法来确定反射的相位，该方法基于这样的概念，即如果函数Delta r(R)满足约束平均值(Delta R)=0和(Delta R)2的平均值=1，则(Delta R)4的电子密度对比度平均值的平均四次方取决于化学成分而不是物理结构。作为进一步的约束，以强度的高斯变迹的形式使用形状归一化，这具有归一化原点处的自相关函数的曲率的效果。我们分析了两个不同组成的立方体样品：对于每个立方体样品，我们生成了与X射线散射数据相一致的所有相组合，并寻找那些(δr)4的平均值与六方相最吻合的相组合。利用相图的良好性质，我们仔细研究了各种参数的影响；我们得出的结论是，被比较的相的化学成分必须相同，X射线散射数据不应该被人为截断，切趾必须是温和的，以便曲率介于对应于两相原始数据的曲率之间。当采取了所有这些预防措施后，(R)4的平均值被发现是显著不变的；这一结论是重要的，因为这项新技术在解决从头算--以及在非常低的分辨率--更普遍感兴趣的结构问题方面可能有用。立方相的结构由按钻石晶格4×4四面体连接的棒状三维网络和一族准球形的不相交胶束组成；棒状和胶束的核心是极性的，空隙由碳氢链(II型结构)填充。所有的尺寸(棒和胶束的直径，在极性/非极界面的每条链的面积)都与体系的化学性质一致。
The phase diagram of the Pseudomonas fluorescens lipid extract is unusual, in the sense that it displays a cubic phase straddled by a hexagonal phase. The hexagonal phase was studied over an extended concentration range, and the reflections were phased on the assumption that the structure contains circular cylinders of known radius. The cubic phase, whose extinction symbol is Fd--, was analyzed by reference to space group No. 227 (Fd3m). The phases of the reflections were determined by using a novel pattern recognition approach, based upon the notion that the average fourth power of the electron density contrast mean value of (delta r)4 is dependent on chemical composition but not on physical structure, provided that the function delta r(r) satisfies the constraints mean value of (delta r) = 0 and mean value of (delta r)2 = 1. As a further constraint, a shape normalization is used, in the form of a Gaussian apodization of the intensities, which has the effect of normalizing the curvature of the autocorrelation function at the origin. We analyzed two cubic samples of different composition: for each of them we generated all the phase combinations compatible with the X-ray scattering data and we searched for those whose mean value of (delta r)4 best agrees with the hexagonal phase. Taking advantage of the favorable properties of the phase diagram, we carefully explored the effects of various parameters; we concluded that the chemical composition of the phases being compared must be identical, that the X-ray scattering data should not be truncated artificially, and that the apodization must be mild so that the curvature takes a value intermediate between those corresponding to the raw data of the two phases. When all these precautions were taken, mean value of (delta r)4 was found to be remarkably invariant; this conclusion is important in view of the possible usefulness of the novel technique in tackling ab initio--and at very low resolution--structural problems of more general interest. The structure of the cubic phase consists of a 3D network of rods joined tetrahedrally 4 by 4 according to a diamond lattice and of a family of quasi-spherical disjointed micelles; the core of the rods and of the micelles is polar, and the interstices are filled by the hydrocarbon chains (structure of type II). All the dimensions (diameter of rods and micelles, area per chain at the polar/apolar interface) are consistent with the chemical properties of the system.(ABSTRACT TRUNCATED AT 400 WORDS)
通过高效薄层色谱和密度测定法分析脑脂质。
影响因子：
6.5
作者：
Macala,LJ;Yu,RK;Ando,S
通讯作者：
Ando,S