Catalytic activity and inhibition of carbonic anhydrase of rat tissues

Carbonic anhydrase activity was studied in stomach and kidney homogenates, and isoenzymes were purified from erythrocytes and livers of male and female rats. Two liver isoenzymes of male and female rats and one erythrocyte isoenzyme had low CO₂ hydration activity. The enzymes of stomach and kidney, one isoenzyme of erythrocytes and one of female rat liver had high CO₂ hydration activity. The esterase activity toward p-nitrophenyl acetate paralleled the CO₂ hydration activity of all the isoenzymes. However, the esterase activity toward β-naphthyl acetate was either absent or did not show any correlation with the CO₂ hydration activity of isoenzymes. Male rat liver carbonic anhydrases were 1000 times less sensitive to sulfonamides than female rat liver carbonic anhydrases for the inhibition both of CO₂ hydration and esterase activity. Male rat liver carbonic anhydrases were as sensitive to inhibition by monovalent anions as were the female rat liver carbonic anhydrases. It is concluded that the active site of carbonic anhydrases from male rat liver is more hydrophilic than the active site of carbonic anhydrase from female rat liver or other tissues of the rat.