title: Oxidation of 2-thioflavins by peroxides. Formation of flavin 2-S-oxides.
abstract: The reaction of 2-thioriboflavin (sulfur replacing the oxygen substituent at position 2 alpha) with hydrogen peroxide at pH approximately 10 leads to a blue flavin (lambda max = 565 nm) which was purified in stable, homogeneous form. Titrations of 2-thioflavins with m-chloroperoxybenzoic acid also yield the same blue flavins with consumption of 1 eq of peracid. Anaerobic reduction of the blue flavin by sodium dithionite requires 4e- eq, and leads to formation of 1,5-dihydro-2-thioflavin. Oxidation of the latter with O2 restores the original 2-thioflavin. pH titration of the blue flavin shows two pKa values of 2.4 and 6.6, with no apparent ionization in the pH range 8-11. These results suggest that the blue flavin is a flavin 2-S-oxide. The visible absorption spectra of flavin 2-S-oxides show a pronounced dependence on solvent polarity. This property suggests that these flavin analogs may be useful hydrophilic/hydrophobic probes of flavoprotein active sites. Flavin 2-S-oxides can be oxidized further to the 2-sulfinate and 2-sulfonate analogs, some properties of which are described.
mesh_terms: D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004227:Dithionite / Q000378:metabolism; D005415:Flavins / Q000378:metabolism*; D005420:Flavoproteins / Q000378:metabolism; D010084:Oxidation-Reduction; D010545:Peroxides / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D005415:Flavins; D005420:Flavoproteins; D010545:Peroxides; D004227:Dithionite; C038134:blue flavin