On the red blood cell Ca2+-pump: An estimate of stoichiometry
- 28 Downloads
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.
KeywordsInorganic Phosphate Plasma Membrane MgCl2 CaCl2 Human Physiology
Unable to display preview. Download preview PDF.
- Fiske, C.H., SubbaRow, Y. 1925. The colorimetric determination of phosphorus.J. Biol. Chem. 66:375Google Scholar
- Gilman, A., Philips, F.S., Koelle, E.S., Allen, R.P., St. John, E. 1946. The metabolic reduction and nephrotoxic action of tetrathionate in relation to a possible interaction with sulfhydryl compounds.Am. J. Physiol. 147:115Google Scholar
- Roy, A.B., Trudinger, P.A. 1970. The Biochemistry of Inorganic Compounds of Sulphur. Ch. 2, p. 19. Cambridge University Press, LondonGoogle Scholar
- Sarkadi, B., Szász, I., Gárdos, G. 1976. The use of ionophores of rapid loading of human red cells with radioactive cations for cation-pump studies.J. Membrane Biol. 26:357Google Scholar
- Schatzmann, H.J. 1973. Dependence on calcium concentration and stoichiometry of the calcium pump in human red cells.J. Physiol. (London) 235:551Google Scholar
- Schatzmann, H.J. 1975. Active calcium transport and Ca2+-activated ATPase in human red cells.In: Current Topics in Membranes and Transport. F. Bronner and A. Kleinzeller, editors. p. 125. Academic Press, New YorkGoogle Scholar
- Schatzmann, H.J., Vincenzi, F.F. 1969. Calcium movements across the membrane of human red cells.J. Physiol. (London) 201:369Google Scholar