Hydrolytically dechlorinates atrazine to hydroxyatrazine. Dechlorinates also simazine, and desethylatrazine but is not active with terbutylazine or desethyldesisopropylatrazine (PubMed:8759853). Has no deaminase activity with melamine (PubMed:8759853, PubMed:22768133). atrazine + H2O = chloride + H(+) + hydroxyatrazine Binds 1 Fe(2+) ion per subunit (PubMed:12450410, PubMed:25760618). In vitro can also use Co(2+) or Mn(2+) (PubMed:12450410). Atrazine dechlorination rates are reduced by aminoatrazine but dechlorination is not inhibited by either melanine or CAAT (2-chloro-4,6-diamino-s-triazine). kcat is 11 sec(-1) with atrazine as substrate. Xenobiotic degradation; atrazine degradation; cyanurate from atrazine: step 1/3. Homohexamer; trimer of dimers. AtzA and melamine deaminase (TriA) from Acidovorax citrulli strain NRRL B-12227 are 98% identical but catalyze distinct biochemical reactions. Enzymes differ by only 9 amino acids. These 9 amino acid differences between TriA and AtzA represent a short evolutionary pathway connecting enzymes catalyzing physiologically relevant deamination and dehalogenation reactions, respectively (PubMed:11274097). Potential evolutionary trajectories between AtzA and TriA have been constructed, and catalytic activities of the intermediates along those trajectories have been characterized (PubMed:22768133). Belongs to the metallo-dependent hydrolases superfamily. ATZ/TRZ family.