The esterase activity of carbonic anhydrase (CA) was investigated in mussels sampled at 24 locations along the Croatian coast of Adriatic Sea. The gills were the target tissue because the respiratory, ionic transport and pH regulatory enzyme function of CA and its potential usage as biomarkers of environmental pollution was the main topic. Total esterase activity was measured in cytosolic fraction by colorimetric end-point reaction using p-nitrophenyl acetate as enzyme substrate. CA activity was estimated by the same enzymatic reaction using acetazolamide as a specific CA inhibitor. The results of total esterase activities in winter (March; all sites average value 0.137±0.057) were lower than determined for summer season (August; 0.153±0.036) at almost all investigated locations. CA activities determined in gills of mussel sampled in winter ranged from 1.75% to 24.65% of total esterase activities and in summer samples were lower (0.83 to 13.45%). Although recent research showed potential application of CA activity in bioassay and biomarker in pollution studies, further research is needed. Here we report a short-term simple colorimetric microplate method which can be applied for analyses of large numbers of samples. Furthermore in this study we characterized full length coding sequence (cDNA) of M. galloprovincialis carbonic anhydrase II (CAII). The CAII cDNA (with the 5’ and 3’ untranslated regions) is 1317 bp long. The putative open reading frame encodes a polypeptide of 256 amino acids, with a theoretical pI/Mw 5.87/28.416 kDa and conserved domains (active site and zinc binding site).
