Nitrotoluenes biotransformation

VERTICAL EXPANSION OF THE PATHWAYS FOR MONONITROBENZOATES AND PUTATIVE HOSTS FOR EXPLOITATION OF THE CATABOLIC POTENTIAL OF ENZYMES ABLE TO BIOTRANSFORM NITROTOLUENES... 

TNT is readily absorbed through skin, especially when skin is moist. It is excreted in urine more than in feces some is found in bile. The major biotransformation reaction is nitroreduction and, to a lesser extent, oxidation. The main metabolite formed by nitroreduction seems to be 4-amino-2,6-dinitrotoluene (4-ADNT). Other metabolites include 2-amino-4,6-dinitrotoluene (2-ADNT), 2,4-diamino-6-nitrotoluene, and 2,6-diamino-4-nitrotoluene. The metabolites are excreted in the urine as glucuronide conjugates and in the free form. Ring oxidation products of TNT such as trinitrobenzylalcohol, trinitrobenzoic acid, and simultaneous oxidation and reduction metabolites such as 2,6-dinitro-4-amino-benzylalcohol and 2,6-dinitro-4-amino-m-cresol are of less importance. Untransformed TNT is also excreted in the urine. ADNT and TNT concentrations were found in workers in explosives factories. 4-ADNT excretion was reported to be complete within 3M days after exposure. However, another study reported detectable urine concentration of ADNT in explosives workers even after 17 days away from the workplace. 

The biotransformation of nitrotoluenes has been examined in toluene-grown cells of pseudomonads which contain a toluene dioxygenase. The products depended on the relative position of the substituents and clearly illustrated the various metabolic reactions that may be mediated by this dioxygenase 2-nitro- and 3-nitrotol-uene were converted into the corresponding benzyl alcohols, whereas 4-nitrotoluene produced 3-methyl-6-nitrocatechol and 2-methyl-5-nitrophenol (Figure 6.113) (Robertson et al. 1992). 

TNT is most commonly biotransformed by reduction of the nitro groups. By the sequential addition of two electrons, a nitro group is reduced to a nitroso, a hydroxylamino, and hnally to an amino group. Through successive reductions of the three nitro groups, many bacterial species sequentially transform TNT to aminodi-nitrotoluene, diaminonitrotoluene, and finally triaminotoluene (TAT). However, in some bacterial cultures hydroxylamino-substituted compounds persist without the production of amino-substituted compounds. Two monoamino isomers, 2-amino-4,... 

Trinitrotoluene (TNT) and its biotransformation products (2,6-diamino-4-nitrotoluene, 2,4-diamino-6-nitrotoluene, 4-amino-2,6-dinitrotoluene, and 2-amino-4,6-dinitrotoluene) were baseline resolved on tandem Cig/cyanopropyl columns (A = 230nm) using a 60.5/25/14.5 water/methanol/THF mobile phase. Elution was complete in <20 min [182]. 

Potential of Toluene-Oxidizing Enzymes for Biotransformation of Nitrotoluenes... 

Figure 3. Biotransformation of nitrotoluene by toluene monooxygenase, produced by the TOL plasmid pWWO...

Figure 4. Biotransformation of toluene and nitrotoluenes by the chromosomally encoded toluene dioxygenase of Pseudomonas sp. FI.

The initial step in the metabolism of TNT by nearly every organism seems to be reduction (8-13, 18, 19, 27, 32, 51, 52, 59, 63, 64, 74, 87, 96, 97). Most often nitrotoluenes are biotransformed to aromatic amines (31, 40) through a series of reduction steps as described by Yamashima et al. (99). The para nitro group of TNT is usually reduced preferentially to the ortho group. A second series of reductions predominantly leads to the formation of 2,4-diaminonitrotoluene (2,4-DAT). Reduction of the third nitro group usually only occurs under anaerobic conditions (55). Under aerobic conditions, hydroxylamino metabolites are sufficiently long lived to lead to the formation of azoxy compounds or polymers which are products of condensation of hydroxylamino and nitroso dinitrotoluenes (56). 

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