Potassium ion-activated hydrolysis of p-nitrophenyl phosphate in pancreatic islet-cell membranes.
Hydrolysis of p-nitrophenyl phosphate was measured in a fraction enriched in plasma membranes from pancreatic islets of non-inbred ob/ob mice. Hydrolysis was stimulated by K+ (10mM) in the pH range 5--10; a small peak of K+-induced activation was observed between pH7.5 and 8. Both the K+-induced activation and the hydrolysis in the absence of K+ were Mg2+-dependent; maximum activation was obtained with 10mM-K+ plus 5 mM-Mg2+. Rb+ was as effective an activator as K+. Ouabain was inhibitory, the effect being inversely related to the K+ concentration; 0.1--0.2mM-ouabain caused about 50% inhibition in the presence of 1 mM-K+, but had no demonstrable effect in the presence of 4--5mM-K+. The K+-stimulated activity was markedly inhibited by 0.1mM-ATP, 35--140 MM-Na+, or 0.01 mM-p-chloromercuribenzenesulphonic acid. Similarities to Rb+ accumulation suggest that catalysis of univalent cation flow in pancreatic beta-cells may be coupled to a phosphoryl-transfer reaction with ATP as natural substrate or regulator.
D009597:4-Nitrophenylphosphatase / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002412:Cations / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D009596:Nitrophenols / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D012413:Rubidium / Q000494:pharmacology
D002412:Cations; D009596:Nitrophenols; D010042:Ouabain; D000255:Adenosine Triphosphate; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D008274:Magnesium; D012413:Rubidium; D011188:Potassium