Аннотация:Na,K-ATPase is purified and isolated in the form of open membrane fragments. The fragments are capacitively coupled to a black lipid membrane, and this arrangement can be used to study ion movements and kinetics without interference from other ion-transporting proteins in the membrane. Relaxation techniques, especially the ATP-concentration jump technique, are introduced and discussed, as well as the admittance-measurement method that allows obtaining kinetic parameters without forcing the ion pump out of its actual steady state. These experimental approaches have been used very successfully to investigate ion movements in the cytoplasmic and extracellular ion access channel of the Na,K-ATPase that are the essential reactions steps of the pump cycle in which the ions are transferred within the protein from one side of the membrane to the other. Theoretical approaches to describe and analyze experimental results are introduced