Binding of the third Na+ ion to the cytoplasmic side of the Na,K-ATPase is electrogenic.
A new experimental setup was constructed to allow parallel measurements of total internal reflection fluorescence and of capacitance changes in Na,K-ATPase-containing membranes. Effects correlated with cytoplasmic sodium binding to Na,K-ATPase were investigated. Ion binding-induced fluorescence changes of the electrochromic dye RH421 in membrane fragments adsorbed on a transparent capacitative electrode corresponded perfectly to capacitance increases detected by a lock-in technique. From these electric measurements it was possible to estimate a dielectric coefficient of about 0.25 for the electrogenic binding of the third Na+ ion. Binding of K+ to cytoplasmic sites was electroneutral.
Domaszewicz
W
W
Department of Biology, University of Konstanz, Germany.
Apell
H
H
D000818:Animals; D001665:Binding Sites; D003593:Cytoplasm / Q000201:enzymology* / Q000502:physiology; D004553:Electric Conductivity; D004563:Electrochemistry; D007668:Kidney / Q000201:enzymology / Q000502:physiology; D008564:Membrane Potentials; D008954:Models, Biological; D008956:Models, Chemical; D011817:Rabbits; D012964:Sodium / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D012965:Sodium Chloride / Q000737:chemistry; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D013050:Spectrometry, Fluorescence
D012965:Sodium Chloride; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase