Effects of ATP on the Steady-State Level of the Phosphoenzyme of Pig Kidney Na+/K+-ATPase

  • P. J. Schwarzbaum
  • R. C. Rossi
  • S. B. Kaufman
  • P. J. Garrahan

Abstract

The Albers-Post model for the hydrolysis of ATP by the Na+/K+-ATPase postulates that the release of Pi from ATP is preceded by the formation of at least two conformers of a phosphoenzyme as shown in Scheme I During steady-state, the rate of ATP hydrolysis (vi) will be equal to the net rate of any of the elementary steps of the reaction. Hence in the absence of Pi:
$$v_i = k_{\textit{31}} \times E_\textit{2}P = K_{\textit{23}} \times E_\textit{1}P - K_{\textit{32}} \times E_\textit{2}P$$
$$\textup{Since} EP_T = E_\textit{1}P + E_\textit{2}P, \textup{it follows that}: EP_T =\frac{E_\textit{2}P \times (K_{\textit{31}} + k_{\textit{32}} +k_{\textit{23}})}{k_{\textit{23}}} \\ \textup{and therefore} \frac{v_i}{EP_T} = \frac{k_{\textit{31}} \times k_{\textit{23}}}{k_{\textit{31}} + k_{\textit{32}} + k_{\textit{23}}}$$
Equations essentially similar to Eqn (2), will apply for reaction schemes including any amount of additional phosphoenzymes. Eqn (2) evinces one of the fundamental features of the class of models shown in Scheme 1, i.e., that the ratio between steady-state activity and steady-state level of total phosphoenzyme will be independent of the rate of phosphorylation and of the transitions among the different dephosphoforms of the ATPase.
Scheme 1.

The Albers Post model for ATP hydrolysis by the Na+/K+ATPase postulates that ATP binds to the dephosphoforms of the ATPase and that release of inorganic phosphate is preceded by the sequential formation of at least two phosphoenzymes.

Keywords

Hydrolysis EDTA MgCl2 Argentina Aires 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    Jensen J, Nørby JG, Ottolenghi P (1984) Sodium and potassium binding to the sodium pump of pig kidney: stoichiometry and affinities evaluated from nucleotide-binding behaviour. J Physiol 346: 219–241PubMedGoogle Scholar
  2. 2.
    Klodos I, Nørby JG (1988) Does ATP affect the interconversion and the dephosphorylation of the phosphoenzymes of the Na,K-pump?. In: Skou JC, Nørby JG, Maunsbach AB, Esmann M (eds) The Na+, K+-pump. Part A: Molecular aspects, Allan R. Liss, New York, pp.321–326.Google Scholar

Copyright information

© Dietrich Steinkopff Verlag GmbH & Co. KG, Darmstadt 1994

Authors and Affiliations

  • P. J. Schwarzbaum
    • 1
  • R. C. Rossi
    • 1
  • S. B. Kaufman
    • 1
  • P. J. Garrahan
    • 1
  1. 1.Departamento de Química Biológica. Facultad de Farmacia y BioquímicaUniversidad de Buenos AiresBuenos AiresArgentina

Personalised recommendations