Carbonic anhydrase enzyme catalyzes the reversible inter-conversion of CO2 and HCO3. The enzyme is crucial for the osmotic balance and acid–base regulation in the fish. It is well-known that gills of fish play the most important role in acid–base relevant ion transfer, the transfer of H+ and/or HCO3, for the maintenance of systemic pH. Many researches have shown that fish are the species that is the most susceptible to environmental toxins. In addition, these toxins firstly encounter the gill tissue in fish. In this study, the carbonic anhydrase enzyme was purified 198.6-folds with 58.8% yield from Shabut Fish (Barbus grypus) gill tissue by Sepharose-4B-L-tyrosine-sulfanilamide affinity column. The specific activity was determined as 2.92 EU/mg protein. The molecular weight determined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis was found to be about 29.9 kDa. Inhibitory effects of some pesticides (Spinosad and Dimethoate) and metal ions (Al3+, Cu2+, Ba2+, Fe2+, Mn2+, Se2+) were examined on the purified carbonic anhydrase enzyme. Inhibition graphics were drawn in order to find the IC50 values of metals and pesticides showing inhibition. The kinetic parameters of this enzyme were determined for its esterase activity, with 4-nitrophenyl acetate as substrate
