X-Ray Absorption Near Edge Spectroscopy of Sulfur in Biomolecules: Two Examples from Glutathione and Insulin

G. Cinquea, G. Bellisolab, M. Colombattib and E. Burattini c aI.N.F.N. - Laboratori Nazionali di Frascati, via Fermi 40, 00044 Frascati, Italy bDepartment of Pathology, Section of Immunology, University of Verona Policlinico GB Rossi, P. le L.A. Scuro, 10, 37134 Verona, Italy cDepartment of Informatics, Faculty of Science, University of Verona, Ca' Vignal 2, 37134 Verona, Italy

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Received: 2005 20 05;

Although a minor constituent of cell and tissues, sulfur is an essential element to fulfil a wide range of biological processes, and it is present in the functional groups of many biomolecules that participate to redox reactions in vivo. Cysteine, one of the two S-containing aminoacids present in proteins, contains sulfur in fully reduced form and its thiol group can undergo a range of reactions under physiological conditions. X-ray absorption spectroscopy represents a unique tool to speciate the redox state of sulfur in biomolecules because of the known strong correlation between oxidation state and absorption edge energy shift (over 10 eV). Moreover, a rich X-ray absorption near edge structure is related to the chemical structures of S-containing biomolecules, as well as significant spectral changes due to biochemical action. The formation of a disulfide bond, i.e. a covalent linkage between the S atoms of two cysteine residues, or its reduction were investigated only indirectly in biomolecules. X-ray absorption spectroscopy experiments at the sulfur K-edge were performed at the soft X-ray beamline in Frascati using the wiggler source of the 0.51 GeV storage ring DAΦNE. X-ray absorption near edge structure data were collected to distinguish in situ between S-thiol and disulfide on model protein systems. Such preliminary results confirm this technique as a unique probe of sulfur chemistry in vivo. Quantitative speciation of S-metabolites can be foreseen in biological tissues with no chemical manipulations of the specimen.

DOI: 10.12693/APhysPolA.109.335 PACS numbers:78.70.Dm, 87.64.Gb