Paraoxon, 4-nitrophenyl phosphate and acetate are substrates of α- but not of β-, γ- and ζ-carbonic anhydrases

Carbonic anhydrases (CAs, EC 4.2.1.1) belonging to α-, β-, γ- and ζ-classes and from various organisms, ranging from the bacteria, archaea to eukarya domains, were investigated for their esterase/phosphatase activity with 4-nitrophenyl acetate, 4-nitrophenyl phosphate and paraoxon as substrates. Only α-CAs showed esterase/phosphatase activity, whereas enzymes belonging to the β-, γ- and ζ-classes were completely devoid of such activity. Paraoxon, the metabolite of the organophosphorus insecticide parathione, was a much better substrate for several human/murine α-CA isoforms (CA I, II and XIII), with kcat/KM in the range of 2681.6–4474.9 M−1 s−1, compared to 4-nitrophenyl phosphate (kcat/KM of 14.9–1374.4 M−1 s−1).

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