title: Salinity adaptation of HCO3--dependent ATPase activity in the gills of blue crab (Callinectes sapidus).
abstract: A bicarbonate-dependent ATPase (EC 3.6.1.3) was found in microsomal preparations from blue crab gills. When the crabs were transferred to low salinity (200 mosmolal) from seawater (1000 mosmolal), the HCO3- dependent ATPase increased in all gill pairs, reaching its new steady state in 2 weeks. The greatest increase occurred in the sixth and seventh gill pairs (approx. 2.5-fold). Maximal enzyme activity was observed at an Mg2+ concentration of 2 mM and an optimal pH of 7.8. The apparent Ka for HCO3- was found to be 8.9 mM. Kinetic analysis showed that low-salinity adaptation increased the Vmax without altering the Km for ATP. When the microsomes from high-salinity crab gills were treated with detergent or assayed at different temperatures, the total enzyme activity did not reach the activity levels after adaptation to low salinity. These results suggest that the alteration of HCO3- -ATPase activity may be due to synthesis, rather than modulation of membranes or of the existing enzyme activity.
mesh_terms: D000251:Adenosine Triphosphatases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D027321:Anion Transport Proteins; D003386:Brachyura / Q000201:enzymology*; D017301:Ca(2+) Mg(2+)-ATPase; D005880:Gills / Q000201:enzymology*; D008861:Microsomes / Q000201:enzymology; D009994:Osmolar Concentration; D012965:Sodium Chloride / Q000494:pharmacology; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D027321:Anion Transport Proteins; D012965:Sodium Chloride; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; C031652:anion-sensitive ATPases