title: Rb(+) occlusion stabilized by vanadate in gastric H(+)/K(+)-ATPase at 25°C.
abstract: Despite its similarity with the Na(+)/K(+)-ATPase, it has not been possible so far to isolate a K(+)-occluded state in the H(+)/K(+)-ATPase at room temperature. We report here results on the time course of formation of a state containing occluded Rb(+) (as surrogate for K(+)) in H(+)/K(+)-ATPase from gastric vesicles at 25°C. Alamethicin (a pore-forming peptide) showed to be a suitable agent to open vesicles, allowing a more efficient removal of Rb(+) ions from the intravesicular medium than C(12)E(8) (a non-ionic detergent). In the presence of vanadate and Mg(2+), the time course of [(86)Rb]Rb(+) uptake displayed a fast phase due to Rb(+) occlusion. The specific inhibitor of the H(+)/K(+)-ATPase SCH28080 significantly reduces the amount of Rb(+) occluded in the vanadate-H(+)/K(+)-ATPase complex. Occluded Rb(+) varies with [Rb(+)] according to a hyperbolic function with K(0.5)=0.29±0.06mM. The complex between the Rb(+)-occluded state and vanadate proved to be very stable even after removal of free Mg(2+) with EDTA. Our results yield a stoichiometry lower than one occluded Rb(+) per phosphorylation site, which might be explained assuming that, unlike for the Na(+)/K(+)-ATPase, Mg(2+)-vanadate is unable to recruit all the Rb(+)-bound to the Rb(+)-occluded form of the Rb(+)-vanadate-H(+)/K(+)-ATPase complex.
authors.affiliation: Instituto de Química y Fisicoquímica Biológicas and Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina. mmontes@qb.ffyb.uba.ar
authors.forename: Mónica R
authors.initials: MR
authors.lastname: Montes
authors.forename: Alejandro J
authors.initials: AJ
authors.lastname: Spiaggi
authors.forename: José L E
authors.initials: JL
authors.lastname: Monti
authors.forename: Flemming
authors.initials: F
authors.lastname: Cornelius
authors.forename: Claus
authors.initials: C
authors.lastname: Olesen
authors.forename: Patricio J
authors.initials: PJ
authors.lastname: Garrahan
authors.forename: Rolando C
authors.initials: RC
authors.lastname: Rossi
mesh_terms: D000408:Alamethicin / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D003902:Detergents / Q000737:chemistry; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017506:H(+)-K(+)-Exchanging ATPase / Q000737:chemistry*; D007477:Ions; D008024:Ligands; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D012413:Rubidium / Q000737:chemistry*; D013270:Stomach / Q000201:enzymology*; D013552:Swine; D013696:Temperature; D013997:Time Factors; D014638:Vanadates / Q000737:chemistry*
chemical_list: D003902:Detergents; D004791:Enzyme Inhibitors; D007477:Ions; D008024:Ligands; D010455:Peptides; D000408:Alamethicin; D014638:Vanadates; D017506:H(+)-K(+)-Exchanging ATPase; D012413:Rubidium