Enzymatic reduction of azo and indigoid compounds

Abstract

A customer- and environment-friendly method for the decolorization azo dyes was developed. Azoreductases could be used both to bleach hair dyed with azo dyes and to reduce dyes in vat dyeing of textiles. A new reduced nicotinamide adenine dinucleotide-dependent azoreductase of Bacillus cereus, which showed high potential for reduction of these dyes, was purified using a combination of ammonium sulfate precipitation and chromatography and had a molecular mass of 21.5 kDa. The optimum pH of the azoreductase depended on the substrate and was within the range of pH 6 to 7, while the maximum temperature was reached at 40 degrees C. Oxygen was shown to be an alternative electron acceptor to azo compounds and must therefore be excluded during enzymatic dye reduction. Biotransformation of the azo dyes Flame Orange and Ruby Red was studied in more detail using UV-visible spectroscopy, high-performance liquid chromatography, and mass spectrometry (MS). Reduction of the azo bonds leads to cleavage of the dyes resulting in the cleavage product 2-amino-1,3 dimethylimidazolium and N approximately 1 approximately ,N approximately 1 approximately -dimethyl-1,4-benzenediamine for Ruby Red, while only the first was detected for Flame Orange because of MS instability of the expected 1,4-benzenediamine. The azoreductase was also found to reduce vat dyes like Indigo Carmine (C.I. Acid Blue 74). Hydrogen peroxide (H(2)O(2)) as an oxidizing agent was used to reoxidize the dye into the initial form. The reduction and oxidation mechanism of Indigo Carmine was studied using UV-visible spectroscopy.

Electrochemical reduction of disperse orange 1 textile dye at a boron-doped diamond electrode

“…The intestinal microflora metabolizes ingested azo dyes to colorless aromatic amines, using NAD(P)H-dependent azoreductases [11][12][13][14]. Although the dyes can be reduced in the mammalian liver to form aromatic amines, the intestinal microflora is probably primarily responsible for the in vivo reduction of azo dyes [10][11][12][13][14]. Chequer et al [15] demonstrated the mutagenicity of DO1 using the micronucleus assay in human lymphocytes and in the HepG2 human liver cell line.…”

“…The human intestinal microbiota plays a role in the degradation of azo dyes, with azo reduction being the most important reaction with respect to their toxicity and mutagenicity [10]. The intestinal microflora metabolizes ingested azo dyes to colorless aromatic amines, using NAD(P)H-dependent azoreductases [11][12][13][14]. Although the dyes can be reduced in the mammalian liver to form aromatic amines, the intestinal microflora is probably primarily responsible for the in vivo reduction of azo dyes [10][11][12][13][14].…”

Spectrophotometric evaluation of the behavior of disperse red 1 dye in aqueous media and its interaction with calf thymus ds-DNA

“…17 They can be metabolized by azoreductase enzymes at the gastrointestinal cells, producing free aromatic amines that are potentially carcinogenic and mutagenic. 13,[18][19][20] Several studies have indicated that azo dyes can cause DNA damage. 4,[21][22][23][24] DNA plays a key role in cell proliferation, synthesis of proteins, and transcription of genetic information in living cells.…”

“…13,[18][19][20] Several studies have indicated that azo dyes can cause DNA damage. 4,[21][22][23][24] DNA plays a key role in cell proliferation, synthesis of proteins, and transcription of genetic information in living cells.…”

BTI1, an Azoreductase with pH-Dependent Substrate Specificity

“…Ammoniumazo-1 (Am-Azo-1), citrus yellow, orange G, Ponceau BS, and ruby red were inert to reduction with BTI10 (pHs 5.5 to 8.3). A lack of reduction of the last two is surprising because they have been reduced by other azoreductases (2,3,8,9). At pH 6, BTI10 efficiently reduced MeO, o-methyl red (o-MeR), and BHQ-10 but flame orange (FO) and Janus green B (JGB) only poorly.…”