Sulfur K-Edge X-Ray Absorption Spectroscopy: A Spectroscopic Tool to Examine the Redox State of S-Containing Metabolites in vivo

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 95; no. 11; pp. 6122 - 6127
• Main Authors: Rompel, Annette, Cinco, Roehl M., Latimer, Mathew J., McDermott, Ann E., Guiles, R. D., Quintanlha, Alexandre, Krauss, Ronald M., Sauer, Kenneth, Yachandra, Vittal K., Klein, Melvin P.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 26-05-1998; National Acad Sciences; National Academy of Sciences; The National Academy of Sciences
• Subjects: Absorption spectra; Amino acids; Biological Sciences; Blood plasma; Disulfides; Erythrocytes; Erythrocytes - metabolism; Humans; Inflection points; Line spectra; Oxidation-Reduction; Physics; Plasma - metabolism; Plasma spectra; Scientific imaging; Spectrometry, X-Ray Emission - methods; Sulfoxides; Sulfur; Thiols
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.95.11.6122

The sulfur K-edge x-ray absorption spectra for the amino acids cysteine and methionine and their corresponding oxidized forms cystine and methionine sulfoxide are presented. Distinct differences in the shape of the edge and the inflection point energy for cysteine and cystine are observed. For methionine sulfoxide the inflection point energy is 2.8 eV higher compared with methionine. Glutathione, the most abundant thiol in animal cells, also has been investigated. The x-ray absorption near-edge structure spectrum of reduced glutathione resembles that of cysteine, whereas the spectrum of oxidized glutathione resembles that of cystine. The characteristic differences between the thiol and disulfide spectra enable one to determine the redox status (thiol to disulfide ratio) in intact biological systems, such as unbroken cells, where glutathione and cyst(e)ine are the two major sulfur-containing components. The sulfur K-edge spectra for whole human blood, plasma, and erythrocytes are shown. The erythrocyte sulfur K-edge spectrum is similar to that of fully reduced glutathione. Simulation of the plasma spectrum indicated 32% thiol and 68% disulfide sulfur. The whole blood spectrum can be simulated by a combination of 46% disulfide and 54% thiol sulfur.