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Beaugé, Luis

Breakdown of Na+/K+‐exchanging ATPase phosphoenzymes formed from ATP and from inorganic phosphate during Na+‐ATPase activity. : Response to Na+ and K+ ions : Response to Na<sup>+</sup> and K<sup>+</sup> ions

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  • Medientyp: E-Artikel
  • Titel: Breakdown of Na+/K+‐exchanging ATPase phosphoenzymes formed from ATP and from inorganic phosphate during Na+‐ATPase activity. : Response to Na+ and K+ ions : Response to Na<sup>+</sup> and K<sup>+</sup> ions
  • Beteiligte: Beaugé, Luis
  • Erschienen: Wiley, 2001
  • Erschienen in: European Journal of Biochemistry
  • Sprache: Englisch
  • DOI: 10.1046/j.1432-1033.2001.02499.x
  • ISSN: 0014-2956; 1432-1033
  • Schlagwörter: Biochemistry
  • Entstehung:
  • Anmerkungen:
  • Beschreibung: <jats:p>The reactivity towards Na<jats:sup>+</jats:sup> and K<jats:sup>+</jats:sup> of Na<jats:sup>+</jats:sup>/K<jats:sup>+</jats:sup>‐ATPase phosphoenzymes formed from ATP and P<jats:sub>i</jats:sub> during Na<jats:sup>+</jats:sup>‐ATPase turnover and that obtained from P<jats:sub>i</jats:sub> in the absence of ATP, Na<jats:sup>+</jats:sup> and K<jats:sup>+</jats:sup> was studied. The phosphoenzyme formed from P<jats:sub>i</jats:sub> in the absence of cycling and with no Na<jats:sup>+</jats:sup> or K<jats:sup>+</jats:sup> in the medium showed a biphasic time‐dependent breakdown. The fast component, 96% of the total EP, had a decay rate of about 4 s<jats:sup>−1</jats:sup> in K<jats:sup>+</jats:sup>‐free 130 mm Na<jats:sup>+</jats:sup>, and was 40% inhibited by 20 m<jats:sc>m</jats:sc> K<jats:sup>+</jats:sup>. The slow component, about 0.14 s<jats:sup>−1</jats:sup>, was K<jats:sup>+</jats:sup> insensitive. Values for the time‐dependent breakdown of the phosphoenzymes obtained from ATP and from P<jats:sub>i</jats:sub> during Na<jats:sup>+</jats:sup>‐ATPase activity were indistinguishable from each other. In K<jats:sup>+</jats:sup>‐free medium containing 130 m<jats:sc>m</jats:sc> Na<jats:sup>+</jats:sup>, the decays followed a single exponential with a rate constant of 0.45 s<jats:sup>−1</jats:sup>. The addition of 20 m<jats:sc>m</jats:sc> K<jats:sup>+</jats:sup> markedly increased the decays and made them biphasic. The fast components had a rate of ≈ 220 s<jats:sup>‐1</jats:sup> and accounted for 92–93% of the total phosphoenzyme. The slow components decayed at a rate of about 47–53 s<jats:sup>−1</jats:sup>. A second group of experiments examined the reactivity towards Na<jats:sup>+</jats:sup> of the E<jats:sub>2</jats:sub>P forms obtained with ATP and P<jats:sub>i</jats:sub> when the enzyme was cycling. In both cases, the rate of dephosphorylation was a biphasic function of [Na<jats:sup>+</jats:sup>]: inhibition at low [Na<jats:sup>+</jats:sup>], with a minimum at about 5 mm Na<jats:sup>+</jats:sup>, followed by recovery at higher [Na<jats:sup>+</jats:sup>]. Although qualitatively similar, the phosphoenzyme formed from P<jats:sub>i</jats:sub> showed slightly less inhibition and more pronounced recovery. These results indicate that forward and backward phosphorylation during Na<jats:sup>+</jats:sup>‐ATPase turnover share the same intermediates.</jats:p>
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