Intensity determination by profile-fitting applied to precession photographs
Intensity determination by profile-fitting applied to precession photographs
复制标题
通过应用于进动照片的轮廓拟合来确定强度
DOI：
10.1107/s0021889874010430
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发表时间：
1974
影响因子：
6.1
通讯作者：
G. C. Ford
中科院分区：
文献类型：
--
作者：
G. C. Ford
本文提出了一种轮廓拟合算法，用于从旋进照片中确定X射线衍射强度。假设膜上的每个反射在围绕其中心的二维点阵列上具有相同的轮廓或缩放的强度分布。反射的积分强度是在缩放模型轮廓和反射的光密度测量之间给出最佳拟合的比例因子。计算强度的系统误差从模型和观察到的配置文件之间的差异进行评估，并为约2%的强反射（约1.5 OD单位）。轮廓拟合减少了可能的随机误差的强度，在光密度测量中产生的误差，一半的值由传统的积分。这种增益对于形成大量蛋白质数据集的弱反射尤其重要。通过该方法处理的膜数据与蛋白质乳酸脱氢酶的衍射仪数据（不对称单位为34000道尔顿）之间的比较表明，膜数据与衍射仪数据以及衍射仪数据集之间一致。 甘油醛-3-磷酸脱氢酶（144000道尔顿的不对称单位）的电影数据的可靠性指数为6%和显着Bijvoet差异测得的汞衍生物的蛋白质。 模型数据的校正方法的非线性效应的电影数据进行评估。结果表明，这些修正给出了显着的改善，只有当数据满足两个条件：他们在很宽的范围内的光密度（至少20 D单位），他们是可靠的（优于4%的可靠性指标）。在这些条件下，扩展版本的汉密尔顿，Rollett和火花缩放算法比其他方法考虑的性能更好。
A profile-fitting algorithm has been applied to the determination of X-ray diffraction intensities from precession photographs. It is assumed that each reflection on the film has the same profile or scaled intensity distribution, over a two-dimensional array of points about its center. The integrated intensity of a reflection is that scale factor which gives the best fit between a scaled model profile and the optical density measurements of the reflection. The systematic error in the calculated intensity was evaluated from the discrepancy between the model and observed profiles and was about 2% for strong reflections (about 1.5 OD units). Profile fitting reduced the likely random error in the intensity, produced by errors in optical density measurements, to half the value given by conventional integration. This gain is especially significant for weak reflections which form the bulk of protein data sets. A comparison between film data processed by this method and diffractometer data for the protein lactate dehydrogenase, (34000 Dalton in asymmetric unit), showed that film data agreed with diffractometer data as well as diffractometer data sets agreed among themselves. Film data for glyceraldehyde-3-phosphate dehydrogenase (144000 Dalton in asymmetric unit) had a reliability index of 6% and significant Bijvoet differences were measured for mercury derivatives of the protein. Methods for the correction for non-linear effects in film data are evaluated for model data. It is shown that these corrections give significant improvement only when the data satisfy two conditions: they extend over a wide range of optical densities (at least 20D units) and they are reliable (better than 4% reliability index). Under these conditions an extended version of the Hamilton, Rollett and Sparks scaling algorithm performs better than the other methods considered.