Understanding the Energy Source for Na+-Ca2+ Exchange after Dephosphorylation Steps of the Na+-ATPase Activity of Na+, K+-ATPase

  • Luis Beaugé
  • Marta Campos
  • Roberto Pezza

Abstract

Living cells maintain a steady different ionic compositions between the intra and extracellular compartments. This implies electrochemical gradients for many ionic species which are of large magnitudes; in turn, it requires mechanisms that keep a delicate balance between inward and outward ionic fluxes across the cellular membrane. Dissipating fluxes in favor of an electrochemical gradient are opposed by energy consuming fluxes of the same magnitude. In the case of the so called “pumps” the free energy comes directly from ATP hydrolysis. In the co- and countertransport systems the energy arises from the gradient dissipation of other ionic species (Ullricht, 1979; Tanford, 1983; Aroson, 1985). A paradigmatic case is given by Ca2+ ions. With an electronegative cell interior the intracellular Ca2+ concentration is about 104 times smaller than that at the extracellular fluid. Two mechanisms work in parallel to account for this large electrochemical gradient. The Ca2+ pump and the Na+-Ca2+ exchange. The first takes the required energy from ATP. The second extrudes Ca2+ at the expenses of the free energy stored in the gradient of Na+ across the membrane. Actually, the Na+ gradient is as a generalized energy donor for co- and countertransport of solutes as it is the ATP for ionic pumps. Therefore, the knowledge of the mechanism for the Na+ electrochemical gradient generation is of paramount importance for all non-pumped energy requiring transports mechanism. This chapter deals with a detailed study of some partial reactions of the complex Na+-K+ transport cycle which structure, transport and biochemical identity is the Na+,K+ATPase (Glynn, 1985; Norby & Klodos, 1988; Froehlich & Fendler, 1991).

Keywords

Hydrolysis Magnesium Adenosine Vanadate Expense 

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Copyright information

© Springer Science+Business Media New York 1997

Authors and Affiliations

  • Luis Beaugé
    • 1
  • Marta Campos
    • 1
  • Roberto Pezza
    • 1
  1. 1.División de BiofǐsicaInstituto de Investigación Médica „Mercedes y Martín Ferreyra“CórdobaArgentina

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