title: Ca2+-stimulated, Mg2+-independent ATP hydrolysis and the high affinity Ca2+-pumping ATPase. Two different activities in rat kidney basolateral membranes.
abstract: The Mg2+-dependency of Ca2+-induced ATP hydrolysis is studied in basolateral plasma membrane vesicles from rat kidney cortex in the presence of CDTA and EGTA as Mg2+- and Ca2+-buffering ligands. ATP hydrolysis is strongly stimulated by Mg2+ with a Km of 13 microM in the absence or presence of 1 microM free Ca2+. At free Mg2+ concentrations of 1 microM and lower, ATP hydrolysis is Mg2+-independent, but is strongly stimulated by submicromolar Ca2+ concentrations (Km = 0.25 microM, Vmax = 24 mumol Pi/h per mg protein). The Ca2+-stimulated ATP hydrolysis strongly decreases at higher Mg2+ concentrations. The Ca2+-stimulated Mg2+-independent ATP hydrolysis is not affected by calmodulin or trifluoperazine and shows no specificity for ATP over ADP, ITP and GTP. In contrast, at high Mg2+ concentrations calmodulin and trifluoperazine affect the high affinity Ca2+-ATPase activity significantly and ATP is the preferred substrate. Control studies on ATP-dependent Ca2+-pumping in renal basolaterals and on Ca2+-ATPase in erythrocyte ghosts suggest that the Ca2+-pumping enzyme requires Mg2+. In contrast, a role of the Ca2+-stimulated Mg2+-independent ATP hydrolysis in active Ca2+ transport across basolateral membranes is rather unlikely.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001485:Basement Membrane / Q000201:enzymology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D006868:Hydrolysis; D007668:Kidney / Q000201:enzymology* / Q000648:ultrastructure; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013379:Substrate Specificity
chemical_list: D002147:Calmodulin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium