Chlorohydrolase activity

H20. Mass spectrometry confirmed that the product was [ 0]-hydroxyatrazine and thus the reaction was hydrolytic. More recendy, further mechanistic studies have revealed that atrazine chlorohydrolase coordinates ferrous iron, which is essential for its catalytic activity (29). Incubating atrazine chlorohydrolase with the chelators 1,10-phenanthroline or oxalic acid removed the required metal with concomitant loss of activity. Chlorohydrolase activity was restored by the addition of Fe(II), Mn(II), or Co(II) salts. Electron paramagnetic resonance (EPR) and electronic spectroscopic studies provided data consistent with a 1 1 metal to subunit stoichiometry. In total, the data indicate that atrazine chlorohydrolase is a metalloenzyme, making this the first report of a metal-dependent hydrolytic dehalogenase. 

Figure 19 Models of (a) atrazine chlorohydrolase (AtzA) and (b) melamine deaminase (TriA) catalysis, picturing the catalytic metal functioning in water activation and the side chain of residue 238 (either Asn or Asp), which controls leaving group specificity.

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