Na+,K+-ATPase: Structure, mechanism and regulation of activity

The structure and topology of alpha- and beta-subunits of Na+,K+-ATPase, ol igomeric structure of the enzyme, properties of different isoforms of both subunits and mechanisms of ATP hydrolysis and cation transport are consider ed. The data on the structure of cation-binding sites and ionconductive pat hways of the pump are reviewed. A modifying effect of ATP on Na+,K+-ATPase is analyzed with special attention. The hypothesis that explains the comple x dependence of Na+,K+-ATPase activity on the ATP concentration is presente d, It is based on the Suggestion that protomeric form of the enzyme with hi gh affinity for ATP and its oligomeric form with low affinity for the nucle otide coexist in the membrane. The latter form is charactrized by positive cooperative interactions between the subunits. The data on the phosphorylat ion of Na+,K+-ATPase by protein kinases A and C are considered.