Measurement of soft X-ray absorption spectra of biomolecules in biological environments

已经提出，XANES（X射线吸收近边结构）轮廓中的吸收峰由于其分子特异性而可用于化学绘图。然而，对于生物样本的分子成像，应应用在类似于生物样本的环境中测量的XANES。这项研究提出了XANES测量在水和细胞环境中的软X射线区域。水溶液中生物分子的测量用特制的真空样品室在S-K吸收边测量了含硫氨基酸、三肽和蛋白质的XANES。含SH分子与含SS分子的峰位移进行了区分。此外，位移不依赖于样品的分子大小。基于这些结果，我们显示了应用于（1）估计蛋白质中55含量和（2）检测暴露于氧化应激的样品中谷胱甘肽水平的可能性.哺乳动物细胞和细胞器的测量测量CHO细胞、分离的细胞核和线粒体的干燥颗粒的XANES。在N-K吸收边的XANES峰对应的蛋白质和DNA的细胞，细胞核和线粒体。在Ca-L和S-K吸收边得到了类似的结果。这些结果表明，获得的生物分子的XANES峰可以应用于细胞中的分子成像。此外，这一结论还应在其他吸收边条件下进行检验.用电子变倍管接触显微镜在S-K吸收边测量了细胞核和细胞质的吸收光谱。吸收边结构在两者中都被清楚地观察到。地区这一结果之后将是小的局部区域的XANES测量，它提供了有关细胞中元素的化学状态的信息。

It has been proposed that absorption peaks in XANES (X-ray Absorption Near Edge Structure) profiles can be used for chemical mapping due to their molecular specific nature. However for molecular imaging of biological specimens, XANES which was measured in environments similar to biological specimens should be applied. This study presents XANES measurements in water and cellular environments in the soft X-ray region.1. Measurement for biomolecules in water solutionXANES of sulfur-containing amino acids, tripeptides and proteins were measured at the S-K absorption edge using specimen chamber specially made for the use in vacuum. SH-containing molecules were discriminated from SS-containing molecules by the peak shift. In addition the shift did not depend on the molecular size of the specimens. Based on these results, we showed the possibility to the application of (1) estimation of the 55 content in proteins and (2) detection of glutathione level in specimen exposed to oxidative stress.2. Measurement for mammalian cells and cellular organellesXANES was measured for dried pellets of CHO cells, fractionated nucleus and mitochondria. At the N-K absorption edge XANES peaks corresponding to those of proteins and DNA were found for cells, nucleus and mitochondria. Similar results were obtained at the Ca-L and S-K absorption edges. These results suggest that XANES peaks obtained for biomolecules can be applied to the molecular imaging in a cell. Moreover this conclusion should be tested for other absorption edges.3. Measurement for local regions in a cellAbsorption spectra of nuclear and cytoplasmic regions were measured at the S-K absorption edge using the contact microscopy with an electronic zooming tube. The absorption edge structure was clearly observed in both. areas. This result will be followed by the XANES measurement of small local regions, which provides the information about the chemical states of elements in a cell.