Characterization and inhibition studies of an α-carbonic anhydrase from the endangered sturgeon species Acipenser gueldenstaedti

Abstract

An α-carbonic anhydrase (CA, EC 4.2.1.1) was purified and characterized kinetically from erythrocytes of the sturgeon Acipenser gueldenstaedti, an endangered species. The sturgeon enzyme (AgCA) showed kinetic parameters for the CO₂ hydration reaction comparable with those of the human erythrocytes enzyme hCA II, being a highly active enzyme, whereas its esterase activity with 4-nitrophenyl acetate as substrate was lower. Sulphonamide inhibitors (acetazolamide, sulphanilamide) strongly inhibited AgCA, whereas metal ions (Ag⁺, Zn²⁺, Cu²⁺ and Co²⁺) were weak, millimolar inhibitors. Several widely used pesticides (2,4-dichlorophenol, dithiocarbamates, parathion and carbaryl) were also assayed as inhibitors of this enzyme. The dithiocarbamates were low micromolar AgCA inhibitors (IC₅₀ of 16–18 µM), whereas the other pesticides inhibited the enzyme with IC₅₀s in the range of 102–398 µM. The wide use of dithiocarbamate pesticides may be one of the factors enhancing the vulnerability of this sturgeon species to pollutants.

Keywords::

• Carbonic anhydrase
• sturgeon
• enzyme inhibition
• pesticides
• dithiocarbamate

Acknowledgements

We thank the late Dr. İbrahim OKUMUŞ, for the supply sturgeon red blood cells. We are grateful to Dr. Şükrü Beydemir and Dr. Murat KÜÇÜK for helpful discussions and to Dr. Daniela Vullo for the stopped-flow measurements.

Declaration of interest

This study was supported by Research Fund of Karadeniz Technical University (Project No: 2004, 111. 002. 08) and in part by an EU project of the 6th framework programme (DeZnIT, to CTS).