The distribution and partial characterization of carbonic anhydrase in selected aquatic and terrestrial decapod crustaceans

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Abstract
A sensitive pH‐stat assay was used to determine the distribution in aquatic and terrestrial decapod crustaceans, correlation to osmoregulation, and selected kinetic properties of carbonic anhydrase. In all species the enzyme was concentrated in the gills, and specifically the posterior three or four gill pairs. Activity was highest in the gills of osmoregulating species, and the enzyme could be localized in the areas of the gill lamellae which contained a high density of salt absorbing cells. The enzyme from the blue crab, Callinectes sapidus, exhibits a number of characteristics remarkably similar to the Na+/K+ ATPase from that species. Both enzymes show the same inter‐ and intrabrachial distribution and the same reactions to altered environmental salinity. Branchial CA from both species was inhibited by high concentrations of NaCl and increasing pH. The enzyme showed a temperature optimum of 25°C. On the basis of these initial results, it appears that crustacean gill carbonic anhydrase plays an important role in the blood osmoregulatory process.