title: Thallous ion activation of p-nitrophenylphosphatase of rat myometrium plasma membrane.
abstract: Addition of thallous ion (Tl+) inhibited the spontaneous mechanical activity of rat myometrium in K-free Krebs solutions with an I50 value of 30 microM. The corresponding value for I50 for similar inhibition by addition of K+ was 150 microM. Tl+ as well as K+-activated p-nitrophenylphosphatase (PNPPase) of isolated rat myometrium plasma membrane vesicles. Half maximal activation was caused by 0.47 mM Tl+ or 1.6 mM K+. Maximal enzyme activities obtained using Tl+ and K+ were comparable. The Km values for the substance p-nitrophenylphosphatase using Tl+ (1.24 mM) and K+ (1.46 mM) were also similar. Activation by either ion was inhibited by ouabain, Na+, inorganic phosphate, and vanadate (V +5). The results suggest that Tl+ can substitute for K+ for activation of the Na-K pump of rat myometrium plasma membrane.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation; D005260:Female; D007700:Kinetics; D009215:Myometrium / Q000187:drug effects / Q000201:enzymology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism; D013793:Thallium / Q000494:pharmacology*; D014599:Uterus / Q000201:enzymology*
chemical_list: D012964:Sodium; D013793:Thallium; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D011188:Potassium