Biotransformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) catalyzed by a NAD(P)H: nitrate oxidoreductase from Aspergillus niger

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DOIResolve DOI: http://doi.org/10.1021/es011460a
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TypeArticle
Journal titleEnvironmental Science Technology
Volume36
Issue14
Pages31043108; # of pages: 5
AbstractHexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) can be efficiently mineralized with anaerobic domestic sludge, but the initial enzymatic processes involved in its transformation are unknown. To test the hypothesis that the initial reaction involves reduction of nitro group(s), we designed experiments to test the ability of a nitrate reductase (EC 1.6.6.2) to catalyze the initial reaction leading to ring cleavage and subsequent decomposition. A nitrate reductase from Aspergillus niger catalyzed the biotransformation of RDX most effectively at pH 7.0 and 30 degrees C under anaerobic conditions using NADPH as electron donor. LC/MS (ES-) chromatograms showed the formation of hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and methylenedinitramine as key initial products of RDX, but neither the dinitroso neither (DNX) nor trinitroso (TNX) derivatives were observed. None of the above detected products persisted, and their disappearance was accompanied by the accumulation of nitrous oxide (N20), formaldehyde (HCHO), and ammonium ion (NH4+). Stoichiometric studies showed that three NADPH molecules were consumed, and one molecule of methylenedinitramine was produced per RDX molecule. The carbon and nitrogen mass balances were 96.14% and 82.10%, respectively. The stoichiometries and mass balance measurements supported a mechanism involving initial transformation of RDX to MNX via a two-electron reduction mechanism. Subsequent reduction of MNX followed by rapid ring cleavage gave methylenedinitramine which in turn decomposed in water to produce quantitatively N2O and HCHO. The results clearly indicate that an initial reduction of a nitro group by nitrate reductase is sufficient for the decomposition of RDX.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada; NRC Biotechnology Research Institute
Peer reviewedNo
NRC number44658
NPARC number3539441
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Record identifiera0aadbe8-58c2-4905-8ad3-619693fce343
Record created2009-03-01
Record modified2016-05-09
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