On the Mechanism of Biotransformation of the Anthraquinonic Dye Acid Blue 62 by Laccases

Abstract

Abstract:We used the recombinant CotA-laccase from the bacterium Bacillus subtilis to investigate the biotransformation of the commercial anthraquinonic dye Acid Blue 62. Kinetics of dye biotransformation at pH 6 follow a Michaelis-Menten model. NMR and several MS techniques allowed the identification of intermediates and final products of the enzymatic biotransformation. The main final product obtained, 1-[(4-amino-9,10-dioxo-3-sulfo-9,10-dihydroanthracen-1-yl)diazenyl]-4-cyclohexylamino-9,10-dioxo-9,10-dihydroanthracene-2-sulfonic acid, is formed through the creation of an azo link and has been previously identified as an intermediate compound in the biodegradation of Acid Blue 62 by crude fungal preparations. The identification of 1,4-diamino-9,10-dioxo-3-sulfo-9,10-dihydroanthracene-2-sulfonic acid and of cyclohexanone, in reaction mixtures with CotA-laccase and also its presence in reactions performed with the LAC3 laccase from the fungus Trametes sp. C30, suggest the occurrence of coupling reactions between the intermediate products of dye oxidation. Based on these results, we propose a mechanistic pathway for the biotransformation of Acid Blue 62 by laccases. A bioassay based on the inhibitory effects of the dye and its enzymatic products on the growth of Saccharomyces cerevisiae shows the importance of laccases in reducing dye toxicity.

Dyes—Environmental Impact and Remediation

“…2005;Pereira et al 2009a). Antraquinonic dyes are also an important class of dyes, although there is limited information on their physicochemical or biological degradation, and even less on the molecular mechanisms of transformation (Pereira et a!. 2009b ).…”

“…2009b ). Based on the characterisation of intermediates and fmal products of the reaction, Pereira et al (2009b) described the mechanistic pathway for the biotransformation of the anthraquinonic dye AB62 by the bacterial CotA -laccase.…”

The multicopper oxidase from the archaeon Pyrobaculum aerophilum shows nitrous oxide reductase activity

“…In recent years, we have focused our attention on the study of prokaryotic MCOs, the CotA laccase from Bacillus subtilis and the metallo-oxidase McoA from Aquifex aeolicus, because of their potential for biotechnological application [3][4][5][6][7][8]. Several structure-function relationship studies have been performed, revealing redox properties of the T1 site and providing structural insights into the principal stages of the mechanism of dioxygen reduction at the trinuclear center [9][10][11][12].…”

Synthesis of Azobenzene Dyes Mediated by CotA Laccase

“…Although laccases have been extensively used in the degradation/decolourisation of textile dyes, [24][25][26][27] their use in the synthesis of azo dyes has been much less reported. [28][29][30][31] In the last years, our group have developed several eco-friendly protocols towardst he synthesis of different heteroaromatic compounds using CotA laccase from Bacillus subtilis,a sb iocatalyst in the oxidation of primary aromatic amines. [32][33][34] In these studies, azobenzene derivatives were obtained as secondary products, showingt he feasibility of CotA laccase to produce this type of compounds.…”