The distribution and physiological significance of carbonic anhydrase in vertebrate gas exchange organs

The enzyme carbonic anhydrase (CA) catalyzes the reversible hydration/dehyd ration of CO2 and water, maintaining a near-instantaneous equilibrium among all chemical species involved in the reaction. CA is found in association with all tissue and organ systems involved in the transport and excretion o f CO2, from the site of CO2 production, metabolically active tissue such as muscle, to circulating red blood cells in the vasculature, to the various organs of gas exchange, the lungs and gills. The presence of the enzyme in every fluid compartment along the pathway of CO2 transport appears necessar y in order to allow the dehydration of HCO3- to keep pace with the rapid di ffusion of CO2 across biological membranes. Within the actual organ of gas exchange, CA is compartmentalized in multiple subcellular fractions, with t he specific subcellular localization determining the enzyme's physiological function. (C) 2000 Elsevier Science B.V. All rights reserved.