title: Isolation, cloning and characterization of an azoreductase from the halophilic bacterium Halomonas elongata.
abstract: Azo dyes are a major class of colorants used in various industries including textile, paper and food. These dyes are regarded as pollutant since they are not readily reduced under aerobic conditions. Halomonas elongata, a halophilic bacterium, has the ability to decolorize different mono and di-azo dyes in anoxic conditions. In this study the putative azoreductase gene of H. elongata, formerly annotated as acp, was isolated, heterologously expressed in Escherichia coli, purified and characterized. The gene product, AzoH, was found to have a molecular mass of 22 kDa. The enzyme requires NADH, as an electron donor for its activity. The apparent Km was 63 μM for NADH and 12 μM for methyl red as a mono-azo dye substrate. The specific activity for methyl red was 0.27 μmol min(-1)mg(-1). The optimum enzyme activity was achieved in 50mM sodium phosphate buffer at pH 6. Although increased salinity resulted in reduced activity, AzoH could decolorize azo dye at NaCl concentrations up to 15% (w/v). The enzyme was also shown to be able to decolorize remazol black B as a representative of di-azo dyes. This is the first report describing the sequence and activity of an azo-reducing enzyme from a halophilic bacterium.
authors.affiliation: Extremophiles Laboratory, Department of Microbiology, School of Biology and Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, Tehran, Iran.
authors.forename: Maryam
authors.initials: M
authors.lastname: Eslami
authors.affiliation: Extremophiles Laboratory, Department of Microbiology, School of Biology and Center of Excellence in Phylogeny of Living Organisms, College of Science, University of Tehran, Tehran, Iran.
authors.forename: Mohammad Ali
authors.initials: MA
authors.lastname: Amoozegar
authors.affiliation: Department of Biotechnology, College of Science, University of Tehran, Tehran, Iran. Electronic address: asad@ut.ac.ir.
authors.forename: Sedigheh
authors.initials: S
authors.lastname: Asad
mesh_terms: D003001:Cloning, Molecular; D004396:Coloring Agents / Q000737:chemistry / Q000378:metabolism; D004789:Enzyme Activation; D015870:Gene Expression; D020632:Halomonas / Q000201:enzymology* / Q000235:genetics*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009247:NADH, NADPH Oxidoreductases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D009601:Nitroreductases; D011994:Recombinant Proteins
chemical_list: D004396:Coloring Agents; D011994:Recombinant Proteins; D009247:NADH, NADPH Oxidoreductases; D009601:Nitroreductases; C021106:azoreductase
keywords: Azo dyes; Azoreductase; Halomonas elongata; Halophilic bacterium; Methyl red; NADH