Collect. Czech. Chem. Commun. 1996, 61, 962-972

Oxidation of Azo Dyes by Peroxidase: Additional Evidence of a One-Electron Mechanism of Oxidation of Dimethylaminoazobenzene and Sudan I (Solvent Yellow 14)

Marie Stiborov√°a, Befekadu Asfawa, Eva Freib and Heinz H. Schmeiserb

a Department of Biochemistry, Charles University, 128 40 Prague 2, Czech Republic
b Department of Molecular Toxicology, German Cancer Research Center, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany


In the presence of hydrogen peroxide, peroxidase oxidized aminoazo dyes, the non-aminoazo dye 1-phenylazo-2-hydroxynaphthalene (Sudan I, Solvent Yellow 14), and its C-hydroxy derivatives. The oxidation of azo dyes is a pH-dependent reaction; while slightly acidic conditions are optimal for the aminoazo dyes, a basic pH suits better for Sudan I and its hydroxy derivatives. The oxidation of the carcinogenic Sudan I and dimethylaminoazobenzene catalyzed by peroxidase was investigated in detail. Oxygen consumption was not observed in incubations of peroxidase, azo dyes and hydrogen peroxide. However, oxygen uptake was observed after the addition of glutathione, which indicates that free radical metabolites of these compounds are formed by peroxidase. The results suggest that peroxidase metabolizes Sudan I and dimethylaminoazobenzene through a one-electron oxidation mechanism, giving rise to free radicals. Three of the products of Sudan I oxidation by peroxidase with a hitherto unknown structure were characterized partly by UV/VIS and mass spectroscopy.

Keywords: Azo dyes; Oxidation; Peroxidase; Radicals.