Variable stoichiometry in reconstituted shark Na,K-ATPase engaged in uncoupled efflux.
In liposomes with reconstituted shark Na,K-ATPase produced to contain no internal K+ or Na+ addition of external Na+ and ATP induce an uncoupled Na+ efflux on inside-out oriented pumps which is electrogenic and accompanied by hydrolysis of ATP (Cornelius, F. (1989) Biochem. Biophys. Res. Commun. 160, 801-807). At saturating cytoplasmic Na+ the net-charge translocated per ATP molecule split is compatible with a coupling ratio of Nacyt transported per ATP split of 3:1 at pH greater than or equal to 7.0. However, this ratio decreases to 1.5:1 below pH 7.0. At non-saturating cytoplasmic Na+ the 3:1 stoichiometry is attained at pH 7.0-7.5, whereas outside this range of pH the net-charge translocated per ATP molecule split decreases.
Cornelius
F
F
Institute of Biophysics, University of Aarhus, Denmark.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D004284:Dogfish; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008081:Liposomes; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D008081:Liposomes; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium