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. 1986 Jul 1;237(1):197-206.
doi: 10.1042/bj2370197.

Conformational transitions in the Ca2+ + Mg2+-activated ATPase and the binding of Ca2+ ions

R J Froud, A G Lee

Conformational transitions in the Ca2+ + Mg2+-activated ATPase and the binding of Ca2+ ions

R J Froud et al. Biochem J. .

Abstract

We have studied the fluorescence of the Ca2+ + Mg2+-activated ATPase of sarcoplasmic reticulum labelled with fluorescein isothiocyanate. The change in intensity of fluorescein fluorescence caused by addition of Ca2+ to the labelled ATPase can be interpreted in terms of a two-conformation model for the ATPase, one conformation (E1) having a high affinity for Ca2+, the other (E2) a low affinity. Effects of Ca2+ as a function of pH allow an estimate of the effect of pH on the E1/E2 ratio, consistent with kinetic studies. A model is presented for binding of Ca2+ to the ATPase as a function of pH that is consistent both with the data on the E1/E2 equilibrium and with literature data on Ca2+ binding.

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