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The Journal of the Royal Institute of Thailand Vol. 30 No. 1 Jan.-Mar. 2005 70 Humic Substance Enhanced Anaerobic Reduction of Sulfonated Azo Dyes by Paenibacillus sp. Strain A5 TABLE 1. Properties of sulfonated azo dyes used in this study. a The dyes were provided by Dystar Thai Ltd., and not further purified. The absorption maxima and molar extinction coefficients were determined in Na-K phosphate buffer (50 mM; pH 7.5). Remazol Brilliant Orange 3R a reactive orange 16 17757 495 15.4 Remazol Brilliant Violet 5R a reactive violet 5 18097 557 6.8 Remazol Black B a reactive black 5 20505 595 29.1 Azo dye Generic name C.I. λ max Extinction number (nm) coefficient (mM -1 cm -1 ) FIG. 1. Chemical structure of the sulfonated azo dyes used in this study. B. Remazol Black B N=N HO Na - O 3 SOCH 2 CH 2 O 2 S + H 2 N N=N SO 3 Na + - Na - O 3 SOCH 2 CH 2 O 2 S + C. Remazol Brilliant Violet 5R Na - O 3 SOCH 2 CH 2 O 2 S + Na - O 3 S + N=N Cu SO 3 Na + - NHCOCH 3 NHCOCH 3 A. Remazol Brilliant Orange 3R N=N OH Na - O 3 SOCH 2 CH 2 O 2 S + Na - O 3 S + 2000. The role of (auto) catalysis in the mechanism of an anaerobic azo reduction. Water Sci. Technol. 42 : 301-308. 60. Zenno, S.H.K. Koike, A.N. Kumar, R. Jayaraman, M. tanokura, and K. Saigo. 1996. Biochemical characterization of NfsA, the Escherichia coli majornitrore ductase exhibiting a high amino acid sequence homology to Frp, a Vibrio harveyi flavin oxidoreductase. J. Bacteriol. 178 : 4508- 4514. 61. Zenno, S., H. Koike, M. Tanokura, and K. Saigo. 1996. Gene cloning, purification, and characterization of NfsB, a minor oxygen-insensitive nitroreductase from E. coli, similar in biochemical properties to FraseI, the major flavin reductase in Vibrio fischeri. J. Biochem. 120 : 736-744. 62. Zollinger, H. 1987. Color Chemistry, VCH Verlagesselschaft mbH, Weinham, FDR. SO 3 Na + -