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J. Bacteriol., 08 1996, 4926-4934, Vol 178, No. 16
WC Suen, BE Haigler and JC Spain
2,4-Dinitrotoluene (DNT) dioxygenase from Burkholderia sp. strain DNT
catalyzes the initial oxidation of DNT to form 4-methyl-5-nitrocatechol
(MNC) and nitrite. The displacement of the aromatic nitro group by
dioxygenases has only recently been described, and nothing is known about
the evolutionary origin of the enzyme systems that catalyze these
reactions. We have shown previously that the gene encoding DNT dioxygenase
is localized on a degradative plasmid within a 6.8-kb NsiI DNA fragment
(W.-C. Suen and J. C. Spain, J. Bacteriol. 175:1831-1837, 1993). We
describe here the sequence analysis and the substrate range of the enzyme
system encoded by this fragment. Five open reading frames were identified,
four of which have a high degree of similarity (59 to 78% identity) to the
components of naphthalene dioxygenase (NDO) from Pseudomonas strains. The
conserved amino acid residues within NDO that are involved in cofactor
binding were also identified in the gene encoding DNT dioxygenase. An
Escherichia coli clone that expressed DNT dioxygenase converted DNT to MNC
and also converted naphthalene to (+)-
cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene. In contrast, the E. coli
clone that expressed NDO did not oxidize DNT. Furthermore, the enzyme
systems exhibit similar broad substrate specificities and can oxidize such
compounds as indole, indan, indene, phenetole, and acenaphthene. These
results suggest that DNT dioxygenase and the NDO enzyme system share a
common ancestor.
Copyright © 1996, American Society for Microbiology
2,4-Dinitrotoluene dioxygenase from Burkholderia sp. strain DNT: similarity to naphthalene dioxygenase
AL/EQ-OL, Tyndall Air Force Base, Florida 32403-5323, USA.
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