title: Ca2+-stimulated ATPase activities in the gill of the eel: interactions of Mg2+ ions.
abstract: Enriched plasma membrane preparations of the branchial epithelium of freshwater-adapted eels were used to study adenosine triphosphatase (ATPase) activities insensitive to ouabain and responding to Ca2+ and Mg2+. Ca2+ induced ATP hydrolysis; two kinetics were observed in the presence or absence of chelators, one with a high-affinity site (0.3 microM) and one with a lower affinity site (10-20 microM). The high-affinity Ca2+ site or enzyme had a prerequisite for Mg2+ (endogenous Mg2+ being sufficient to satisfy the Mg2+ need) but was inhibited by exogenous Mg2+ (Ki0.5 less than 10 microM Mg2+). The low-affinity site or enzyme appears to have kinetic parameters comparable to those found for Mg2+-induced ATP hydrolysis. In the absence of Ca2+ ligands and with no exogenous Mg2+, the two Ca2+ sites or enzymes can be considered stimulated. The results are discussed in relation to the branchial ion environment and transport ion capacities.
authors.affiliation: Laboratoire Jean Maetz, Departement de Biologie du Commissariat à l'Energie Atomique, Villefranche-sur-Mer, France.
authors.forename: R
authors.initials: R
authors.lastname: Naon
authors.forename: N
authors.initials: N
authors.lastname: Mayer-Gostan
mesh_terms: D000811:Anguilla; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D005880:Gills / Q000201:enzymology*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D015636:Magnesium Chloride; D009571:Nitrilotriacetic Acid / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D015636:Magnesium Chloride; D004533:Egtazic Acid; D010042:Ouabain; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D009571:Nitrilotriacetic Acid