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J. Bacteriol., 11 1996, 6227-6232, Vol 178, No. 21
U Lendenmann and JC Spain
Most bacterial pathways for the degradation of aromatic compounds involve
introduction of two hydroxyl groups either ortho or para to each other.
Ring fission then occurs at the bond adjacent to one of the hydroxyl
groups. In contrast, 2-aminophenol is cleaved to 2- aminomuconic acid
semialdehyde in the nitrobenzene-degrading strain Pseudomonas
pseudoalcaligenes JS45. To examine the relationship between this enzyme and
other dioxygenases, 2-aminophenol 1,6-dioxygenase has been purified by
ethanol precipitation, gel filtration, and ion exchange chromatography. The
molecular mass determined by gel filtration was 140,000 Da. Sodium dodecyl
sulfate-polyacrylamide gel electrophoresis showed two subunits of 35,000
and 39,000 Da, which suggested an alpha2beta2 subunit structure. Studies
with inhibitors indicated that ferrous iron was the sole cofactor. The Km
values for 2- aminophenol and oxygen were 4.2 and 710 microM, respectively.
The enzyme catalyzed the oxidation of catechol, 6-amino-m-cresol,
2-amino-m- cresol, and 2-amino-4-chlorophenol. 3-Hydroxyanthranilate,
protocatechuate, gentisate, and 3- and 4-methylcatechol were not
substrates. The substrate range and the subunit structure are unique among
those of the known ring cleavage dioxygenases.
Copyright © 1996, American Society for Microbiology
2-aminophenol 1,6-dioxygenase: a novel aromatic ring cleavage enzyme purified from Pseudomonas pseudoalcaligenes JS45
AL/EQL, Tyndall Air Force Base, Florida 32403-5323, USA.
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