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

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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.