The reaction mechanism of Na,K-ATPase: problems regarding the oligomeric/monomeric state and the phosphorylated intermediates of the system.
1. The present overview is concerned with the monomeric/oligomeric structure of Na,K-ATPase and with the number and kinetic competence of the phosphorylated intermediates. 2. The transport system, like many other ion-transporters, seems to be oligomeric in situ. It is, however, uncertain whether the oligomeric structure is of functional importance or not. 3. Phosphorylated intermediates (EP) play a central role in the coupling of ATP-hydrolysis to transport. Occlusion of Na+ takes place concomitantly with EP-formation. 4. Two recent revisionist ideas regarding the phosphorylated intermediates are emphasized: First, there are not two but several different EP-conformations, and second, some of the EP's formed in the presence of Na+ alone are incompetent as intermediates in the Na,K-ATPase reaction. This concept requires a revision of the classical Albers-Post scheme for Na,K-ATPase. 5. It is suggested that the classical notion of two principal conformational states E1 and E2 be abandoned. Instead, one should consider that there are many conformational states of the enzyme protein, partly due to the many different liganded states and partly due to subconformations within each enzyme-ligand complex.
Nørby
J G
JG
Institute of Biophysics, University of Aarhus, Denmark.
D001665:Binding Sites; D002462:Cell Membrane / Q000201:enzymology*; D008968:Molecular Conformation; D010766:Phosphorylation; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000493:pharmacokinetics*
D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase