Human CA II (EC 4.2.1.1) is a zinc metalloenzyme which catalyzes the reversible hydration of carbon dioxide to bicarbonate and hydrogen ions. At least 14 different carbonic anhydrase isoforms were isolated in
higher vertebrates. These isozymes have diversified tissue distribution and subcellular positions and they exist in archaea, Eubacteria, animals and plants. Human CA II has a single polypeptide chain of 259 amino acid residues with a molecular mass of about 29 kDa. Organisms and cellular systems which have adapted to stresses such as high temperature, desiccation, and urea-concentrating environments have responded by concentrating particular organic solutes known as osmolytes. These osmolytes are believed to confer protection to enzyme and other macromolecular systems against such denaturing stresses. In this study, differential scanning alorimetric (DSC) experiments were performed on human carbonic anhydrase (HCA II) in the presence of varying concentrations of the glucose which induced considerable increases in the thermal unfolding transition temperature
(Tm) for HCA II. DSC scan of HCA II in the presence of 5.4 M glucose shows the increases of melting point (Tm) up to 10 °C and also enhances the reversibility of thermal unfolded HCA II up to 20 %. The result of circular dichroism CD experiments indicates an increase of 5°C of Tm. Since CD experiment gives informations about secondary structure while DSC profiles show the stability of ertiary structure. The different Tm obtained from CD and DSC indicates the existence of irreversibility for HCA II
