An alpha-carbonic anhydrase (CA, EC 184.108.40.206) was purified and characterized kinetically from gill of Acipenser gueldenstaedtii as an endangered sturgeon species. The carbonic anhydrase was purified 66-folds with yield 20.7% by Sepharose-4B-L-tyrosine-sulfanilamide affinity column and the specific activity was determined as 222.2 EU/mg protein. K-m and V-max kinetic values for gill carbonic anhydrase were calculated by a Lineweaver-Burk graph using p-nitrophenol acetate (p-NPA) as a substrate, and was defined as 2.5mM and 5 x 10(6) mu M/min, respectively. It was observed that CA from the sturgeon gill in the presence of the sulfanilamide and acetazolamide as an inhibitor had very low IC50 values such as 13.0 and 0.1 mu M, respectively. In addition, it was determined that the enzyme was inhibited by Fe-2+,Fe- Co-2+,Co- Ni2+, and Zn2+-Ba2+ with the IC50 values of 0.2, 1.7, 1.2, and 1.1 mM, respectively.