Artículo
The pathway for spontaneous occlusion of Rb+ in the Na +/K+-ATPase
Gonzalez-Lebrero, Rodolfo Martin
; Kaufman, Sergio Benjamín; Garrahan, Patricio Jose
; Rossi, Rolando Carlos
Fecha de publicación:
12/2008
Editorial:
American Chemical Society
Revista:
Biochemistry
ISSN:
0006-2960
Idioma:
Inglés
Tipo de recurso:
Artículo publicado
Clasificación temática:
Resumen
Occlusion of K+ in the Na+/K+-ATPase can be achieved under two conditions: during hydrolysis of ATP, in media with Na+ and Mg2+, after the K+-stimulated dephosphorylation of E2P (physiological route) or spontaneously, after binding of K+ to the enzyme (direct route). We investigated the sidedness of spontaneous occlusion and deocclusion of Rb+ in an unsided, purified preparation of Na+/K+-ATPase. Our studies were based on two propositions: (i) in the absence of ATP, deocclusion of K+ and its congeners is a sequential process where two ions are released according to a single file mechanism, both in the absence and in the presence of Mg 2+ plus inorganic orthophosphate (Pi), and (ii) in the presence of Mg2+ plus Pi, exchange of K+ would take place through sites exposed to the extracellular surface of the membrane. The experiments included a double incubation sequence where one of the two Rb+ ions was labeled as 86Rb+. We found that, when the enzyme is in the E2 conformation, the first Rb+ that entered the enzyme in media without Mg2+ and Pi was the last to leave after addition of Mg 2+ plus Pi, and vice-versa. This indicates that spontaneous exchange of Rb+ between E2(Rb2) and the medium takes place when the transport sites are exposed to the extracellular surface of the membrane. Our results open the question if occlusion and deocclusion via the direct route participates in any significant degree in the transport of K+ during the ATPase activity.
Palabras clave:
sidedness of occlusion
,
Na/K-ATPase
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Articulos(IQUIFIB)
Articulos de INST.DE QUIMICA Y FISICO-QUIMICA BIOLOGICAS "PROF. ALEJANDRO C. PALADINI"
Articulos de INST.DE QUIMICA Y FISICO-QUIMICA BIOLOGICAS "PROF. ALEJANDRO C. PALADINI"
Citación
Gonzalez-Lebrero, Rodolfo Martin; Kaufman, Sergio Benjamín; Garrahan, Patricio Jose; Rossi, Rolando Carlos; The pathway for spontaneous occlusion of Rb+ in the Na +/K+-ATPase; American Chemical Society; Biochemistry; 47; 22; 12-2008; 6073-6080
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