Shulman R G, Eisenberger P, Blumberg W E, Stombaugh N A
Proc Natl Acad Sci U S A. 1975 Oct;72(10):4003-7. doi: 10.1073/pnas.72.10.4003.
The high intensity x-ray flux from the synchrotron radiation at the Stanford Synchroton Radiation Project has been used to study the extended x-ray absorption fine structure (EXAFS) of the iron-sulfur protein Peptococcus aerogenes rubredoxin. Absorption measurements were made from 7080 eV, which is below the K-edge of iron, to about 650 eV above the edge and structure was obtained over the entire region. By means of a model iron-sulfur compound for evaluating the phase shifts, the variation of the absorption above the edge of lyophilized, oxidized rubredoxin was converted to iron-sulfur distances. The data were fitted with a least squares program to a model in which three distances R3 were kept equal and the fourth R1 was allowed to differ. The mean square error was constant over a region of this parameter space, becoming twice as large at R3 = 2.217, R1 = 2.389 and R3 = 2.268, R1 = 2.108 A. These values, which are the extreme differences allowed by the present data, are definitely closer to being equal than those found by the determination of the x-ray diffraction crystal structure of the similar protein from Clostridium pasteurianum. However, the average distance from our experiment is in excellent agreement with the average distance from the crystal structure determination. Preliminary EXAFS measurements were also made on the oxidized rubredoxin in solution at pH 7.0. The spectra were unchanged, indicating that the average iron-sulfur distance change is less than 0.02 A. Upon reduction the average iron-sulfur bond length increased by about 0.05 A. Since the EXAFS measurements can give accurate determinations of distances in proteins both in crystals and solution, the technique should be widely applicable.
斯坦福同步辐射项目中同步辐射产生的高强度X射线通量已被用于研究铁硫蛋白产气消化球菌红素氧还蛋白的扩展X射线吸收精细结构（EXAFS）。吸收测量是在7080电子伏特（低于铁的K边）到高于边约650电子伏特的范围内进行的，并在整个区域获得了结构。通过一种用于评估相移的模型铁硫化合物，将冻干、氧化的红素氧还蛋白边以上吸收的变化转换为铁硫距离。数据用最小二乘法程序拟合到一个模型中，其中三个距离R3保持相等，第四个距离R1允许不同。在该参数空间的一个区域内，均方误差是恒定的，在R3 = 2.217、R1 = 2.389和R3 = 2.268、R1 = 2.108埃时变为原来的两倍。这些值是当前数据允许的最大差异，肯定比通过测定巴氏梭菌类似蛋白质的X射线衍射晶体结构所发现的值更接近相等。然而，我们实验得到的平均距离与晶体结构测定得到的平均距离非常吻合。还对pH 7.0溶液中的氧化红素氧还蛋白进行了初步的EXAFS测量。光谱没有变化，表明平均铁硫距离变化小于0.02埃。还原后，平均铁硫键长度增加了约0.05埃。由于EXAFS测量可以准确测定晶体和溶液中蛋白质的距离，该技术应该具有广泛的适用性。
