title: A high affinity calcium-stimulated ATPase in synaptic plasma membranes detectable in the presence and absence of exogenous magnesium.
abstract: A Ca2+-stimulated ATPase activity detectable in the presence of submicromolar free Ca2+ was characterized in synaptic plasma membrane preparations. In the absence of exogenous magnesium, Ca2+-stimulated ATPase showed a K0.5 Ca2+ of 0.1 microM, Vmax of 125 nmol Pi/mg per min and a Hill number of 1.2. The addition of 1 mM MgCl2 increased basal ATPase activity by about 10-fold. After this activity had been subtracted, apparent values for Ca2+-stimulated ATPase were 0.033 microM (K0.5 Ca2+), 172 nmol Pi/mg per min (Vmax) with a Hill number of 4. These activities were non-significantly affected by ouabain, sodium azide, theophylline and sodium fluoride. The results obtained indicated that high affinity Ca2+-stimulated ATPase activity could be in synaptic plasma membrane-enriched fraction detected both in the presence and absence of exogenous magnesium. Furthermore, the data indicated that magnesium was required for calcium transport.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D006868:Hydrolysis; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013570:Synaptic Membranes / Q000187:drug effects / Q000201:enzymology*; D013806:Theophylline / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D010042:Ouabain; D000255:Adenosine Triphosphate; D013806:Theophylline; D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D002118:Calcium