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J. Bacteriol., 08 1996, 4894-4900, Vol 178, No. 16
ML de Souza, MJ Sadowsky and LP Wackett
Pseudomonas sp. strain ADP metabolizes atrazine to carbon dioxide and
ammonia via the intermediate hydroxyatrazine. The genetic potential to
produce hydroxyatrazine was previously attributed to a 1.9-kb AvaI DNA
fragment from strain ADP (M. L. de Souza, L. P. Wackett, K. L. Boundy-
Mills, R. T. Mandelbaum, and M. J. Sadowsky, Appl. Environ. Microbiol.
61:3373-3378, 1995). In this study, sequence analysis of the 1.9-kb AvaI
fragment indicated that a single open reading frame, atzA, encoded an
activity transforming atrazine to hydroxyatrazine. The open reading frame
for the chlorohydrolase was determined by sequencing to be 1,419
nucleotides and encodes a 473-amino-acid protein with a predicted subunit
molecular weight of 52,421. The deduced amino acid sequence matched the
first 10 amino acids determined by protein microsequencing. The protein
AtzA was purified to homogeneity by ammonium sulfate precipitation and
anion-exchange chromatography. The subunit and holoenzyme molecular weights
were 60,000 and 245,000 as determined by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis and gel filtration
chromatography, respectively. The purified enzyme in H2(18)O yielded
[18O]hydroxyatrazine, indicating that AtzA is a chlorohydrolase and not an
oxygenase. The most related protein sequence in GenBank was that of TrzA,
41% identity, from Rhodococcus corallinus NRRL B-15444R. TrzA catalyzes the
deamination of melamine and the dechlorination of deethylatrazine and
desisopropylatrazine but is not active with atrazine. AtzA catalyzes the
dechlorination of atrazine, simazine, and desethylatrazine but is not
active with melamine, terbutylazine, or desethyldesisopropylatrazine. Our
results indicate that AtzA is a novel atrazine-dechlorinating enzyme with
fairly restricted substrate specificity and contributes to the microbial
hydrolysis of atrazine to hydroxyatrazine in soils and groundwater.
Copyright © 1996, American Society for Microbiology
Atrazine chlorohydrolase from Pseudomonas sp. strain ADP: gene sequence, enzyme purification, and protein characterization
Department of Biochemistry, University of Minnesota, St. Paul 55108, USA.
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