Abstract
The thermodynamic efficiency of the Ca2+-Mg2+-ATPase of skeletal sarcoplasmic reticulum has been evaluated by comparing the Ca2+ gradient established with the ATP/(ADP*Pi) ratio. The evaluation was made at an external Ca2+ level (4.7 × 10−8 M) which is below theK m value of 7 × 10−8 M. The Mg-ATP and phosphate concentrations were held constant (0.1 mM) and the ADP concentration was varied. Maximal uptake to an internal free Ca2+ concentration of 17 mM was observed at infinite ATP/(ADP*Pi) ratio (absence of ADP). This corresponds to a [Ca2+]i/[Ca2+]0 gradient of 3.6 × 105. A Ca2+ gradient one-half as large was observed at an ATP/(ADP*Pi) ratio of 3.5 × 103 M−1. The square of the Ca2+ gradient is shown to be proportional to the ATP/(ADP*Pi) ratio, for finite values of the latter. The proportionality constant is identical to the equilibrium constant for hydrolysis of ATP (9.02 × 106 M) under these conditions (0.1 mM Mg2+, 30°C). The intrinsic thermodynamic efficiency of the pump is shown to be 100%, with a maximal uncertainty of 3%. The efficiency is lower under less optimal conditions, when the pump is inhibited and passive leak processes compete.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Alberty, R. A. (1968).J. Biol. Chem. 243 1337–1348.
Chiu, V. C. K., and Haynes, D. H. (1980).J. Membr. Biol. 56 219–239.
Chiu, V. C. K., Mouring, D., Watson, B. W., and Haynes, D. H. (1980).J. Membr. Biol. 56 121–132.
DeMeis, L., and Vianna, A. L. (1979).Annu. Rev. Biochem. 48 275–292.
Dixon, D., Corbett, A., and Haynes, D. H. (1982).J. Bioenerg. Biomembr. 14 87–96.
Froehlich, J. P., and Taylor, E. W. (1975).J. Biol. Chem. 250 2013–2021.
Froehlich, J. P., and Taylor, E. W. (1976).J. Biol. Chem. 251 2307–2315.
Guynn, R. W., and Veech, R. L. (1973).J. Biol. Chem. 248 6966–6972.
Hasselbach, W., and Makinose, M. (1963).Biochem Z. 339 94–111.
Hasselbach, W. (1978).Biochim. Biophs. Acta 463 23–53.
Hasselbach, W. (1979).Top. Curr. Chem. 78 1–56.
Haynes, D. H., and Mandveno, A. (1983).J Membr. Biol. 74 25–40.
Inesi, G. (1972).Annu. Rev. Biophys. Bioeng. 1 191–210.
Kanazawa, T., Yamada, S., Yamamoto, T., and Tonomura, Y. (1971).J. Biochem. 70 95–123.
MacLennan, D. H., and Holland, P. C. (1975).Annu. Rev. Biophys. Bioeng. 4 377–404.
Martell, A. E., and Smith, R. M. (1974).Critical Stability Constants, Vol. F: Amino Acids, Plenum Press.
Martonosi, A. N. (1980).Fed. Proc. 39 2401–2402.
Phillips, R. C., George, P., and Rutman, R. J. (1969).J. Biol. Chem. 244 3330–3342.
Rosing, J., and Slater, E. C. (1972).Biochim. Biophys. Acta 267 275–290.
Shikama, K., and Nakamura, K. (1973).Arch. Biochem. Biophys. 157 457–463.
Tada, M., Yamamoto, T., and Tonomura, Y. (1978).Physiol. Rev. 58 1–79.
Tanford, C. (1981).J. Gen. Physiol. 77 223–229.
Veech, R. L., Lawson, J. W. R., Cornell, N. W., and Krebs, H. A. (1979).J. Biol. Chem. 254 6538–6547.
Weber, A., Herz, R., and Reiss, I. (1966).Biochem. Z. 345 329–369.
Author information
Authors and Affiliations
Additional information
Dedicated to Prof. Philip George, University of Pennsylvania, whose instruction, research, and example made this contribution possible.
Rights and permissions
About this article
Cite this article
Trevorrow, K., Haynes, D.H. The thermodynamic efficiency of the Ca2+-Mg2+-ATPase is one hundred percent. J Bioenerg Biomembr 16, 53–59 (1984). https://doi.org/10.1007/BF00744145
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00744145