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  • Title: The crustacean gill (Na+,K+)-ATPase: allosteric modulation of high- and low-affinity ATP-binding sites by sodium and potassium.
    Author: Masui DC, Silva EC, Mantelatto FL, McNamara JC, Barrabin H, Scofano HM, Fontes CF, Furriel RP, Leone FA.
    Journal: Arch Biochem Biophys; 2008 Nov 15; 479(2):139-44. PubMed ID: 18796291.
    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.
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