title: A modle for active transport of sodium and potassium ions as mediated by a tetrameric enzyme.
abstract: A new model is proposed for the system that actively transports sodium and potassium ions across animal-cell membranes. The model is based on the physical and chemical properties of transport-associated adenosine triphosphatase (EC 3.6.1.3) and on the kinetics of ion movements mediated by the system. Transport is postulated to occur by internal transfer of cations across a protein tetramer embedded in the cell membrane. The protein tetramer can exist in either of two forms of identical energy; transport occurs as a result of the sequential "flipping" from one conformation to the other. The conformation change results in the interchanging of the affinities of cation-binding sites associated with different sub-units of the tetramer, with a concomitant splitting of adenosine triphosphate.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001665:Binding Sites; D001693:Biological Transport, Active; D002463:Cell Membrane Permeability; D007700:Kinetics; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium