title: The crustacean gill (Na+,K+)-ATPase: allosteric modulation of high- and low-affinity ATP-binding sites by sodium and potassium.
abstract: The blue crab, Callinectes danae, tolerates exposure to a wide salinity range employing mechanisms of compensatory ion uptake when in dilute media. Although the gill (Na+,K+)-ATPase is vital to hyperosmoregulatory ability, the interactions occurring at the sites of ATP binding on the molecule itself are unknown. Here, we investigate the modulation by Na+ and K+ of homotropic interactions between the ATP-binding sites, and of phosphoenzyme formation of the (Na+,K+)-ATPase from the posterior gills of this euryhaline crab. The contribution of the high- and low-affinity ATP-binding sites to maximum velocity was similar for both Na+ and K+. However, in contrast to Na+, a threshold K+ concentration triggers the appearance of the high-affinity binding sites, displacing the saturation curve to lower ATP concentrations.Further, a low-affinity site for phosphorylation is present on the enzyme. These findings reveal notable differences in the catalytic mechanism of the crustacean (Na+,K+)-ATPase compared to the vertebrate enzyme.
authors.affiliation: Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto 14040-901, SP, Brazil.
authors.forename: D C
authors.initials: DC
authors.lastname: Masui
authors.forename: E C C
authors.initials: EC
authors.lastname: Silva
authors.forename: F L M
authors.initials: FL
authors.lastname: Mantelatto
authors.forename: J C
authors.initials: JC
authors.lastname: McNamara
authors.forename: H
authors.initials: H
authors.lastname: Barrabin
authors.forename: H M
authors.initials: HM
authors.lastname: Scofano
authors.forename: C F L
authors.initials: CF
authors.lastname: Fontes
authors.forename: R P M
authors.initials: RP
authors.lastname: Furriel
authors.forename: F A
authors.initials: FA
authors.lastname: Leone
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D003386:Brachyura / Q000201:enzymology*; D002384:Catalysis; D017136:Ion Transport / Q000502:physiology; D009997:Osmotic Pressure; D010766:Phosphorylation; D011485:Protein Binding / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism; D014714:Vertebrates / Q000378:metabolism
chemical_list: D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase