Inhibition of carbonic anhydrases of rat liver by halides.

The hepatic carbonic anhydrases from male rat are known to differ from those of female rat in being resistant to inhibition by sulfonamides. In the present work the inhibition of carbonic anhydrases from livers of male and female rats by chloride and iodide was studied in the CO2 hydration reaction. The hepatic carbonic anhydrases from male rats were found to be more susceptible to inhibition by halides (I50 and Cl- = 7-15 mM, and I- = 0.7-1.5 mM). On the other hand, the hepatic carbonic anhydrases from female rats were less susceptible to inhibition by halides (I50 for Cl- = 150-250 mM and for I- = 3-10 mM). The presence of bicarbonate increased I50 of both Cl- and I- for liver isoenzymes of both male and female rats by about 2- to 20-fold. The differential susceptibility of carbonic anhydrases from livers of male and female rats to inhibition by halides was in contrast to their susceptibility to inhibition by sulfonamides.