The oligomeric nature of Na/K-transport ATPase.
Since the discovery of Na/K-ATPase, evidence has accumulated to suggest that 1 mol of ATP hydrolysis occurs via the Na(+)-occluded ADP-sensitive phosphoenzyme, the K(+)-sensitive phosphoenzyme and the K(+)-occluded enzyme accompanying active transport of 3Na(+) and 2K(+) according the Post-Albers scheme. However, some controversial issues have arisen concerning whether the functional unit of the enzyme is an alpha beta-protomer or a much higher oligomer, which would be related to the mechanism of transport, either sequential or simultaneous. Detailed studies of oligomer interaction and the reactivity of the enzyme and a comparison of the extent of phosphorylation with ligand-binding capacities in the presence or absence of ATP hydrolysis and others strongly suggest that the functional unit of the enzyme in the membrane is a tetraprotomer, (alpha beta)(4). They also suggest that each reaction intermediate of the Post-Albers scheme, respectively, reflects half of the site property of the intermediate and that another half binds ATP. These data may be useful not only to answer the long-standing question of whether the mechanism functions in the presence of both Na(+) and K(+) but also contribute to a better understanding of the mechanism of P-type pump ATPase in general.
Biological Chemistry Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan. ktan@ccms1.hucc.hokudai.ac.jp
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D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D017136:Ion Transport; D008024:Ligands; D010766:Phosphorylation; D020836:Protein Structure, Quaternary; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D013329:Structure-Activity Relationship
D008024:Ligands; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase