Environmental Engineering Reference
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Figure 6.15 Degradation of 4-(4'-sulfophenylazo)-phenol derivatives by Pyricularia
oryzae laccase [171].
Figure 6.16 Degradation of Reactive Blue 19 by laccase from Polyporus sp. [174].
inhibitory to the reaction. One electron oxidation of phenolic group to
phenoxy radical followed by the cleavage of C-N bond was suggested,
which was proposed by Chivukula and Renganathan [171], but not con-
firmed experimentally.
Michniewicz et al. [173] studied the kinetics of laccase-catalyzed decol-
orization of two anthraquinone (Acid Blue 40 and Acid Blue 62) and two
azo (Reactive Blue 81 and Acid Red 27) dyes and one poly-azo (Direct
Black 22) dye using purified enzyme from a white rot fungus Cerrena
unicolor without redox mediators. Among the dyes tested, Acid Blue 40
was the most preferred toward crude C. unicolor laccase based on the
Michaelis-Menten constant ( K m ). They also found that the decolorization
products were more polar than the parent dyes. More recently, Hadibarata
et al. [174] investigated the degradation pathway of an anthraquinone dye,
Reactive Blue 19, by laccase from Polyporus sp. and detected two degrada-
tion products, which confirmed the cleavage of C-N-C bonds connecting
the anthraquinone ring and the benzene ring (Figure 6.16).
Campos et al. [175] used purified T. hirsuta and S. rolfsii laccases for the
degradation of water insoluble Vat Blue 1 (indigo), which was dispersed in
water. Vat Blue 1 was oxidized by laccase and transformed to isatin (indole-
2,3-dione), which was hydrolyzed and further decomposed into anthra-
nilic acid (2-aminobenzoic acid) (Figure 6.17). The indigo particle size was
reduced by the laccase treatment as well. They found that the dye could be
removed from indigo-stained fabrics using the laccases. The enzyme from
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