title: Solubilization of active (H+ + K+)-ATPase from gastric membrane.
abstract: (H+ + K+)-ATPase-enriched membranes were prepared from hog gastric mucosa by sucrose gradient centrifugation. These membranes contained Mg2+-ATPase and p-nitrophenylphosphatase activities (68 +/- 9 mumol Pi and 2.9 +/- 0.6 mumol p-nitrophenol/mg protein per h) which were insensitive to ouabain and markedly stimulated by 20 mM KCl (respectively, 2.2- and 14.8-fold). Furthermore, the membranes autophosphorylated in the absence of K+ (up to 0.69 +/- 0.09 nmol Pi incorporated/mg protein) and dephosphorylated by 85% in the presence of this ion. Membrane proteins were extracted by 1-2% (w/v) n-octylglucoside into a soluble form, i.e., which did not sediment in a 100 000 X g X 1 h centrifugation. This soluble form precipitated upon further dilution in detergent-free buffer. Extracted ATPase represented 32% (soluble form) and 68% (precipitated) of native enzyme and it displayed the same characteristic properties in terms of K+-stimulated ATPase and p-nitrophenylphosphatase activities and K+-sensitive phosphorylation: Mg2+-ATPase (mumol Pi/mg protein per h) 32 +/- 9 (basal) and 86 +/- 20 (K+-stimulated); Mg2+-p-nitrophenylphosphatase (mumol p-nitrophenol/mg protein per h) 2.6 +/- 0.5 (basal) and 22.2 +/- 3.2 (K+-stimulated); Mg2+-phosphorylation (nmol Pi/mg protein) 0.214 +/- 0.041 (basal) and 0.057 +/- 0.004 (in the presence of K+). In glycerol gradient centrifugation, extracted enzyme equilibrated as a single peak corresponding to an apparent 390 000 molecular weight. These findings provide the first evidence for the solubilization of (H+ + K+)-ATPase in a still active structure.
mesh_terms: D000251:Adenosine Triphosphatases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D002462:Cell Membrane / Q000201:enzymology; D002499:Centrifugation, Density Gradient; D005753:Gastric Mucosa / Q000201:enzymology*; D017506:H(+)-K(+)-Exchanging ATPase; D012995:Solubility; D013552:Swine
chemical_list: D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D017506:H(+)-K(+)-Exchanging ATPase