Application of XANES profiles to X-ray spectromicroscopy for biomedical specimens: Part I. Discrimination of macromolecules with sulfur atoms

XANES spectra of biomacromolecules such as histone, hemoglobin or bovine serum albumin (BSA) were measured in transmission at the S-K absorption edge for comparison with those of sulfur containing low-molecular weight biomolecules with special reference to the dependence on the chemical environment of sulfur. The spectra of dry histone and hemoglobin exhibited a prominent peak at the same energy as that of cysteine and glutathione (GSH), while the BSA spectrum showed an additional peak at a lower energy, which coincided with that of cystine and glutathione disulfide (GSSG). XANES peaks were found at the same energy even in a mammalian cell dry pellet. Spectra in the hydrated state exhibited similar profiles except for a very slight shift of resonance peaks to the lower energy. These results indicate that XANES profiles could be applicable to the mapping of S-C and S-S bonds in dry/hydrated biological systems using a spectromicroscopic technique. In addition, mass absorption coefficients of GSH and GSSG were determined.