title: Delta endotoxin is a potent inhibitor of the (Na,K)-ATPase.
abstract: A 68-kDa protein, delta endotoxin, produced by Bacillus thuringiensis ssp. Kurstaki inhibits ion transport, (Na,K)-ATPase, and K+-p-nitrophenylphosphatase activity catalyzed by the Na+ pump. The Ki for inhibition of the K+-p-nitrophenylphosphatase activity of purified dog kidney (Na,K)-ATPase was approximately 0.37 microM. Delta endotoxin had a similar Ki for inhibition of (Na,K)-ATPase activity when assayed at low Na+ concentration (10 mM) but the inhibition was reversed when high concentrations of Na+ (100 mM NaCl) were added to the assay. Phosphorylation of the active site aspartyl residue with 32PO3-4 was also blocked by delta endotoxin. Ouabain-sensitive 86Rb+ uptake into intact human red blood cells was not inhibited by externally added toxin; however, strophanthidin-inhibitable 22Na+ uptake into inside-out vesicles from red blood cells was completely blocked by delta endotoxin (Ki = 0.73 microM). These data suggest that delta endotoxin must enter the cell before it can inhibit the Na+ pump.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000818:Animals; D001413:Bacillus thuringiensis; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D001665:Binding Sites; D004285:Dogs; D004731:Endotoxins / Q000494:pharmacology*; D004910:Erythrocyte Membrane / Q000378:metabolism; D006460:Hemolysin Proteins; D007668:Kidney / Q000201:enzymology; D008970:Molecular Weight; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D012964:Sodium; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium