The Journal of Membrane Biology

, Volume 41, Issue 4, pp 361–376 | Cite as

On the red blood cell Ca2+-pump: An estimate of stoichiometry

  • F. L. Larsen
  • T. R. Hinds
  • F. F. Vincenzi
Article

Summary

Efflux of Ca2+ from reversibly hemolyzed human red blood cell ghosts was determined by a Ca2+ selective electrode, by atomic absorption spectroscopy, and by the use of45Ca. Hydrolysis of ATP was determined by measurement of inorganic phosphate (Pi). At 25°C, ghosts loaded with CaCl2, MgCl2, Na2ATP, and Tris buffer (pH 7.4) extruded Ca2+, with mean rates ranging from 58.8±3.5 (sd) to 74.7±8.2 (sd) μmoles·liter ghosts−1·min depending on the method of Ca2+ determination. The ratio of Ca2+ transported to Pi released in the presence of ouabain without correction for background ATP splitting was 0.83, 0.83, and 0.80, respectively, for the three methods of Ca2+ determination. Correction for the ATPase activity not associated with Ca2+ transport resulted in a ratio of 0.91:1. In other experiments, the use of La3+ to inhibit the Ca2+-pump allowed an estimate of the ATPase activity associated with Ca2+ extrusion. In the presence of various concentrations of La3+, the ratio of Ca2+ pumped to Pi liberated was 0.86 or 1.02, depending on the method of Ca2+ determination. It is concluded that the stoichiometry of the Ca2+-pump of the RBC plasma membrane is one Ca2+ pumped per ATP hydrolyzed.

Keywords

Inorganic Phosphate Plasma Membrane MgCl2 CaCl2 Human Physiology 

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Copyright information

© Springer-Verlag New York Inc. 1978

Authors and Affiliations

  • F. L. Larsen
    • 1
  • T. R. Hinds
    • 1
  • F. F. Vincenzi
    • 1
  1. 1.Department of Pharmacology, School of MedicineUniversity of WashingtonSeattle

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