Carbonic anhydrase activity inhibition: application in a new environmental bioassay.

Aim: Carbonic anhydrase (CA), a ubiquitous metalloenzyme, catalyses the reversible hydration of CO2 to H+ and HCO3- and plays a fundamental role in a number of physiological processes. Previous studies demonstrated the sensitivity of CA activity to chemical pollutants such as dichlorodiphenyl-dichloroethane (DDT) in birds and cadmium in teleost. The aim of the present work was to investigate the sensitivity of CA isozyme II from bovine erythrocytes to heavy metals, PCBs, and pesticides in view of a possible future applications of CA activity inhibition measurement in biomonitoring field as in vitro bioassay. Methods: CA activity was determined by a modification of a previously described electrometric method: briefly, CA activity units were calculated from the rate of H+ production in the reaction mixture (where CO2 was present as substrate) against a blank containing the specific CA inhibitor acetazolamide. The standardized method is simple, rapid and available to be used for routine measurements. Results: The enzymatic activity was first exposed to pure compounds showing a significant dose-response inhibition by submicromolar concentrations of heavy metal (Cd, Cu and Hg), and ppb concentrations of arochlor and carbaryl. Then, CA activity was exposed to contaminated environmental real samples (elutriates of harbour sediments) showing a dose-response inhibition to increasing concentrations of the elutriates in the reaction mixture, suggesting a specific response of the enzymatic activity to the toxicity of the samples. Results obtained with CA were in agreement with those obtained in the same samples with Brachionus plicatilis toxicity test and Paracentrotus lividus spermiotoxicity test. Conclusion: CA activity showed a high sensitivity to the main classes of pollutants relevant for water chemical contamination. Therefore, obtained results suggest the potentiality of CA activity inhibition measurement for application in the screening of general toxicity of environmental samples.