Influence of intramembrane electric charge on Na,K-ATPase.
Effects of lipophilic ions, tetraphenylphosphonium (TPP+) and tetraphenylboron (TPB-), on interactions of Na+ and K+ with Na,K-ATPase were studied with membrane-bound enzyme from bovine brain, pig kidney, and shark rectal gland. Na+ and K+ interactions with the inward-facing binding sites, monitored by eosin fluorescence and phosphorylation, were not influenced by lipophilic ions. Phosphoenzyme interactions with extracellular cations were evaluated through K(+)-, ADP-, and Na(+)-dependent dephosphorylation. TPP+ decreased: 1) the rate of transition of ADP-insensitive to ADP-sensitive phosphoenzyme, 2) the K+ affinity and the rate coefficient for dephosphorylation of the K-sensitive phosphoenzyme, 3) the Na+ affinity and the rate coefficient for Na(+)-dependent dephosphorylation. Pre-steady state phosphorylation experiments indicate that the subsequent occlusion of extracellular cations was prevented by TPP+. TPB- had opposite effects. Effects of lipophilic ions on the transition between phosphoenzymes were significantly diminished when Na+ was replaced by N-methyl-D-glucamine or Tris+, but were unaffected by the replacement of Cl- by other anions. Lipophilic ions affected Na-ATPase, Na,K-ATPase, and p-nitrophenylphosphatase activities in accordance with their effects on the partial reactions. Effects of lipophilic ions appear to be due to their charge indicating that Na+ and K+ access to their extracellular binding sites is modified by the intramembrane electric field.
Klodos
I
I
Institute of Biophysics, University of Aarhus, Denmark.
Fedosova
N U
NU
Plesner
L
L
D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology / Q000502:physiology*; D007668:Kidney / Q000201:enzymology; D008564:Membrane Potentials; D010766:Phosphorylation; D012491:Salt Gland / Q000201:enzymology; D012754:Sharks; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
D000244:Adenosine Diphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase