Kinetics and inhibition of membrane-bound carbonic anhydrase from canine renal cortex.

The membrane-bound carbonic anhydrase (carbonate hydro-lyase, EC 4.2.1.1) in the canine renal cortex has been characterized in terms of its CO2 hydration kinetics and inhibition by sulfonamides and inorganic anions. Comparing these properties with those of the renal cytoplasmic and the human red cell B and C isozymes, it appears that the membrane enzyme is quite different from the soluble carbonic anhydrases. The turnover number of the particulate enzyme is about 3-times lower than that of the cytoplasmic enzyme. The membrane-bound enzyme is also different from its cytoplasmic counterpart in being more resistant against inhibition, particularly against Cl-. Microsomes from the renal cortex were purified to yield luminal and anti-luminal fractions. Carbonic anhydrase activity was found in both. The luminal and anti-luminal carbonic anhydrases appeared similar in terms of their kinetic properties and susceptibility to inhibition.