title: Interactions of K+ with (Na,K)-ATPase orientation of K+-phosphatase sites studied with inside-out red cell membrane vesicles.
abstract: Inside-out membrane vesicles from human red cells were used to investigate the side specificity of K+ interactions with the K+-activated phosphatase, a partial reaction of the (Na, K)-ATPase. In the absence of Na+ and ATP, K+ at moderate affinity sites at the extravesicular surface (cytoplasmic K+) stimulates activity, whereas intravesicular K+ (K+ normally at the extracellular surface) is without effect. In contrast, under conditions of phosphorylation of (Na, K)-ATPase (Na+ and ATP present), K+ ions acting at high affinity sites at both surfaces are required. It is concluded that an enzyme x K complex is involved in K+-activated phosphatase activity and that it is formed either by interaction of cytoplasmic K+ with the dephosphoenzyme, or as a consequence of extracellular K+ binding and dephosphorylation of the phosphoenzyme formed in the presence of Na+ plus ATP.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000097:blood; D000255:Adenosine Triphosphate / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000201:enzymology*; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D066298:In Vitro Techniques; D010710:Phosphates / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D010710:Phosphates; D014634:Valinomycin; D000255:Adenosine Triphosphate; D012964:Sodium; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium