title: Inhibition by lead ion of Electrophorus electroplax (Na+ + K+)-adenosine triphosphatase and K+-p-nitrophenylphosphatase.
abstract: Inorganic lead ion in micromolar concentrations inhibits Electrophorus electroplax microsomal (Na+ + K+)-adenosine triphosphatase ((Na+ + K+)-ATPase) and K+-p-nitrophenylphosphatase (NPPase). Under the same conditions, the same concentrations of PbCl2 that inhibit ATPase activity also stimulate the phosphorylation of electroplax microsomes in the absence of added Na+. Enzyme activity is protected from inhibition by increasing concentrations of microsomes, ATP, and other metal ion chelators. The kinetics follow the pattern of a reversible noncompetitive inhibitor. No kinetic evidence is elicited for interactions of Pb2+ with Na+, K+, Mg2+, ATP, or p-nitrophenylphosphate. Na+- ATPase, in the absence of K+, and (Na+ + K+)-NPPase activity at low [K+] are also inhibited. ATP inhibition of NPPase is not reversed by Pb2+. The calculated concentrations of free [Pb2+] that produce 50% inhibition are similar for ATPase and NPPase activities. Pb2+ may act at a single independent binding site to produce both stimulation of the kinase and inhibition of the phosphatase activities.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D004557:Electric Organ / Q000201:enzymology*; D004593:Electrophorus; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D007854:Lead / Q000494:pharmacology*; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
chemical_list: D007854:Lead; D012964:Sodium; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D000251:Adenosine Triphosphatases; D011188:Potassium