The crustacean gill (Na+,K+)-ATPase: allosteric modulation of high- and low-affinity ATP-binding sites by sodium and potassium.
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.
Masui
D C
DC
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.
Silva
E C C
EC
Mantelatto
F L M
FL
McNamara
J C
JC
Barrabin
H
H
Scofano
H M
HM
Fontes
C F L
CF
Furriel
R P M
RP
Leone
F A
FA
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
D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase