Ca-stimulated Mg dependent ATPase activity in a plasma membrane enriched fraction of bovine corneal epithelium.
In a subcellular plasma membrane enriched fraction of bovine corneal epithelium, Ca2+ stimulated Mg2+ dependent ATPase activity was characterized. This membrane fraction was more than 5-fold and 4-fold enriched with 5'-nucleotidase and alkaline phosphatase activities, respectively, relative to the 100,000 X g pellet. With 250 microM ATP, maximum stimulation of a high affinity form of Ca2+ stimulated Mg2+ dependent ATPase activity was obtained with 1.7 microM free Ca2+. This activation required no exogenously added Mg2+ and was unaffected by either 0.1 mM ouabain, 3 microM ruthenium red, 20 mM sodium azide or 0.2 microgram/ml oligomycin. Exogenous calmodulin (6 microM) elicited a 53% increase in this activity which was completely inhibited by 300 microM trifluoperazine (TFP). These effects of calmodulin and TFP are consistent with the notion of a plasma membrane origin for this activity and also suggest that this activity could be a basis for the regulation of intracellular Ca2+ activity in the submicromolar range.
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D005591:Chemical Fractionation; D003315:Cornea / Q000201:enzymology*; D004492:Edetic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004848:Epithelium / Q000201:enzymology; D007700:Kinetics
D002147:Calmodulin; C005390:CDTA; D004492:Edetic Acid; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases