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Direct determination of crystallographic phases for diffraction data from lipid bilayers. II. Refinement of phospholipid structures.

机译:直接测定晶体相以分析来自脂双层的衍射数据。二。精制磷脂结构。

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摘要

Using a systematic approach for the acceptance of crystallographic phase assignment, based on the evaluation of triplet structure invariants, electron and x-ray diffraction data from phospholipid multilamellar arrays are analyzed by direct methods. After calculation of Fourier maps with a partial set of phased structure factor magnitudes, the structure is refined in real space by flattening of the hydrocarbon region of the bilayer and an optimal solution is sought either by the calculation of [delta rho 4] suggested by Luzzati, where rho is the structure density or by a test of density smoothness [magnitude of delta rho/ delta r magnitude of], where r positions are located along the normal to the lamellar surface. Reanalyses of previously determined structures sometimes lead to new conclusions (e.g., a possible similarity of the electron density profile for DL-DMPE and L-DMPE, and a clear indication of the fatty acid adduct in the mixed L-DPPC/palmitic acid bilayer). Because of presumed secondary scattering perturbations (primarily to the least intense reflections), the refinements of the electron diffraction intensities are less easily evaluated than those carried out with x-ray diffraction data.
机译:使用一种接受结晶相分配的系统方法,基于三重态结构不变量的评估,通过直接方法分析了磷脂多层阵列的电子和X射线衍射数据。在计算了具有部分相结构因子量集的傅立叶图之后,通过平整双层烃的区域来在真实空间中精炼结构,并通过Luzzati建议的[δrho 4]计算来寻求最佳解决方案,其中rho是结构密度或通过密度平滑度的测试[delta rho的幅度/ delta r幅度的大小],其中r位置沿薄层表面的法线定位。对先前确定的结构进行的重新分析有时会得出新的结论(例如,DL-DMPE和L-DMPE的电子密度分布可能相似,并且清楚地表明了混合的L-DPPC /棕榈酸双层中的脂肪酸加合物) 。由于假定的二次散射扰动(主要是最不强烈的反射),与用X射线衍射数据进行的电子衍射强度的细化相比,评估起来不那么容易。

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