Carbonic anhydrase (CA; EC 22.214.171.124) was purified from the gill of the teleost fish Dicentrarchus labrax (European seabass). The purification procedure consisted of a single step affinity chromatography on Sepharose 4B-tyrosine-sulfanilamide. The enzyme was purified 84.9-fold with a yield of 58%, and a specific activity of 838.9 U/mg proteins. It has an optimum pH at 8.0; an optimum temperature at 10 degrees C. The kinetic parameters of this enzyme were determined for its esterase activity, with 4-nitrophenyl acetate (NPA) as substrate. The following anions, H2NSO3-, I , SCN , NO3- , NO2- , N-3(-) , Br , Cl , SO42- , and F showed inhibitory effects on the enzyme. Sulfamic acid, iodide, and thiocyanate exhibited the strongest inhibitory action, in the micromolar range (K(i)s of 87-187 mu M). NO3- , NO2- and N-3(-) were moderate inhibitors, whereas other anions showed only weak actions. All tested anions inhibited the enzyme in a competitive manner. Our findings indicate that these anions inhibit the fish enzyme in a similar manner to other a-CAs from mammals investigated earlier, but the susceptibility to various anions differs significantly between the fish and mammalian CAs. (C) 2010 Elsevier Ltd. All rights reserved.