Interaction of magnesium with the sodium pump of the human red cell.
1. In broken red cell membranes, Mg2+ inhibition of Na+,K+-adenosine-5'-triphosphatase (Na+,K+-ATPase) activity was partially competitive with MgATP. Mg2+ inhibition of Na+,K+-ATPase activity was uncompetitive with K+ in broken red cell membranes, and Mg2+ inhibition of ouabain-sensitive K+ influx in K+-free resealed ghosts was uncompetitive with external K+. 2. When Na+,K+-ATPase activity was measured at relatively high K+ concentration, Mg2+ inhibition was partially competitive with Na+. Mg2+ inhibition of ouabain-sensitive K+ influx in K+-free resealed ghosts was competitive with cell Na+. Magnesium was a more effective inhibitor of the uncoupled Na+ efflux in low-Na+ ghosts than in high-Na+ ghosts. 3. These findings indicate that Mg2+ inhibition results from combination of the ion with the enzyme form E2K at high intracellular Na+ and K+, and from combination with the form E1 at low intracellular Na+ and K+. 4. In ghosts containing high concentrations of MgPO4, inhibition of the K+-K+ exchange by Mg2+ was more effective at high than at low nucleotide concentrations. At high MgPO4 and low Mg2+ concentration the activity of the exchange increased monotonically with nucleotide concentration, but at a higher Mg2+ concentration, nucleotide activation of the exchange was biphasic: the K+-K+ exchange rate increased, reached a maximum, and then decreased with increasing nucleotide concentration.
Sachs
J R
JR
Department of Medicine, State University of New York, Stony Brook.
D000255:Adenosine Triphosphate / Q000037:antagonists & inhibitors / Q000097:blood; D001693:Biological Transport, Active / Q000187:drug effects; D003864:Depression, Chemical; D004910:Erythrocyte Membrane / Q000378:metabolism*; D006801:Humans; D008274:Magnesium / Q000097:blood* / Q000494:pharmacology; D008433:Mathematics; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000493:pharmacokinetics; D012964:Sodium / Q000097:blood*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000097:blood
D010042:Ouabain; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium