title: Effects of the ATP, ADP and inorganic phosphate on the transport rate of the Na+,K+-pump.
abstract: (Na+ + K+)-ATPase from kidney outer medulla was incorporated into artificial dioleoylphosphatidylcholine vesicles. In the reconstituted system the pump can be activated by adding ATP to the external medium. ATP-driven potassium extrusion by the Na+,K+-pump was studied using a voltage-sensitive dye in the presence of valinomycin. ADP strongly reduced the turnover rate of the pump with a concentration for half-maximal inhibition of cD,1/2 = 0.1 mM. cD,1/2 was found to be virtually independent of ATP concentration, indicating that the inhibition is non-competitive with respect to ATP. The non-competitive inhibition by ADP can be explained on the basis of the Post-Albers reaction cycle of the Na+,K+-pump, assuming that the main action of ADP is the reversal of the phosphorylation step. A similar 'product inhibition' was observed with inorganic phosphate, but at much higher concentrations (cP,1/2 = 14 mM).
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D007679:Kidney Medulla / Q000201:enzymology*; D007700:Kinetics; D008081:Liposomes; D008433:Mathematics; D008954:Models, Biological; D010710:Phosphates / Q000494:pharmacology*; D010713:Phosphatidylcholines; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
chemical_list: D008081:Liposomes; D010710:Phosphates; D010713:Phosphatidylcholines; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; C017251:1,2-oleoylphosphatidylcholine