Characterization and inhibition studies of an α-carbonic anhydrase from the endangered sturgeon species Acipenser gueldenstaedti

An alpha-carbonic anhydrase (CA, EC 4.2.1.1) was purified and characterized kinetically from erythrocytes of the sturgeon Acipenser gueldenstaedti, an endangered species. The sturgeon enzyme (AgCA) showed kinetic parameters for the CO2 hydration reaction comparable with those of the human erythrocytes enzyme hCA II, being a highly active enzyme, whereas its esterase activity with 4-nitrophenyl acetate as substrate was lower. Sulphonamide inhibitors (acetazolamide, sulphanilamide) strongly inhibited AgCA, whereas metal ions (Ag+, Zn2+, Cu2+ and Co2+) were weak, millimolar inhibitors. Several widely used pesticides (2,4-dichlorophenol, dithiocarbamates, parathion and carbaryl) were also assayed as inhibitors of this enzyme. The dithiocarbamates were low micromolar AgCA inhibitors (IC50 of 16-18 mu M), whereas the other pesticides inhibited the enzyme with IC(50)s in the range of 102-398 mu M. The wide use of dithiocarbamate pesticides may be one of the factors enhancing the vulnerability of this sturgeon species to pollutants.