Interaction of sodium and potassium ions with Na+, K+-ATPase. III. Cooperative effect of ATP and Na+ on complete release of K+ from E2K.
The effects of Na+ and ATP on the K+ binding to Na+, K+-ATPase were investigated by the centrifugation method with radioactive K+ in the absence of Mg2+. In the presence of 10 microM 43KCl, 0.6 and 10 mM Na+ decreased the amount of bound K+ to one-half and zero, respectively. On the other hand, 10 microM and 10 mM ATP decreased the amount of K+ to 60 and 25-40%, respectively. When the combined effect of ATP and Na+ was tested, 10 microM ATP decreased the Na+ concentration giving half-maximal inhibition of the K+ binding to one-third, showing synergistic inhibition by both ligands, though increase in ATP concentration seemed to depress the inhibitory effect of Na+. The synergistic inhibition by ATP and Na+ suggests that the release of K+ from E2K is not completed by the binding of ATP alone but is completed by the binding of Na+ in addition to ATP during the cycle of Na+, K+-dependent ATP-hydrolysis as well as ion-transport.
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D004285:Dogs; D007679:Kidney Medulla / Q000201:enzymology / Q000648:ultrastructure; D008274:Magnesium / Q000378:metabolism; D008861:Microsomes / Q000201:enzymology; D010042:Ouabain / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D012965:Sodium Chloride; D010042:Ouabain; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium