title: Properties of potassium activated p-nitrophenyl phosphatase of plasma membranes isolated from rat stomach muscle.
abstract: The plasma membrane-enriched fraction isolated from smooth muscle of rat gastric fundus was found to contain a substantial level of potassium-stimulated p-nitrophenylphosphatase activity (K-pNPPase), and its subcellular distribution closely resembled that of other plasma membrane enzyme markers. The kinetic profile of K-pNPPase and its sensitivity toward ouabain and vanadate confirmed the identification of this activity with the partial reaction of the sodium pump. The specific activity of K-pNPPase and its sensitivity to ouabain was significantly increased in the presence of saponin, indicating that part of this activity is latent when assayed on native membrane preparation. K-pNNPase was sensitive to the presence of calcium ions in the assay medium. The Ca2+-inhibition of K-pNNPase was accompanied by increased sensitivity of the enzyme to ouabain. On the other hand, calmodulin and Ca antagonists had no effect on K-pNPPase activity nor its sensitivity to calcium.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005748:Gastric Fundus / Q000378:metabolism; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D003902:Detergents; D007473:Ion Channels; D010042:Ouabain; D012964:Sodium; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium; D002118:Calcium