Atrazine chlorohydrolase

Reaction

AtzA is an atrazine-dechlorinating enzyme with fairly restricted substrate specificity and plays a main role in the hydrolysis of atrazine to hydroxyatrazine in soils and groundwater. Atrazine Hydroxyatrazine is a hydrolase (an enzyme that catalyzes the hydrolysis of a chemical bond ), which acts on halide bonds in C-halide compounds. In 1993, pseudomonas sp. strain ADP was shown to degrade atrazine to cyanuric acid via three steps, the first of which is a dechlorination.

Genetics

De Souza, Sadowsky and Wackett were able to determine the nucleotide and amino acid sequence in 1996. The gene coding for the enzyme shows 99% similarity between bacteria. In fact there is only a 9-nucleotide difference, directly corresponding to the amino acid differences. The nucleotide differences are unlikely to cause a conformational change in the enzyme but rather site-specific alterations. This seems logical considering the remarkable similarity in the substrates and the relatively short period of evolution.

Specificity

AtzA was shown to displace fluoride as well as chlorine but not azido, cyano, methoxy, which are of similar size and electronegativity, or thiomethyl or amino groups. The inability of AtzA to perform deamination makes it unique within its superfamily, amidohydrolases. Furthermore, atrazine is not degraded by melamine deaminase and it does not inhibit melamine deaminase activity suggesting the active site is not specific for atrazine.

References

References

1. (October 2000). "Substrate specificity of atrazine chlorohydrolase and atrazine-catabolizing bacteria". Appl Environ Microbiol.
2. (April 2001). "Melamine deaminase and atrazine chlorohydrolase: 98 percent identical but functionally different". J. Bacteriol..