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. 1987 Oct;84(20):7094–7098. doi: 10.1073/pnas.84.20.7094

Sarcoplasmic reticulum calcium pump: a model for Ca2+ binding and Ca2+-coupled phosphorylation.

C Tanford 1, J A Reynolds 1, E A Johnson 1
PMCID: PMC299236  PMID: 2959957

Abstract

The conventional alternating access model for Ca2+ transport by the sarcoplasmic reticulum Ca2+ pump is modified, partly on the basis of the proposed MacLennan-Green domain structure for the Ca2+-pump protein. The present model divides the uptake state (E1) of the protein into three substates, differing in the condition of the Ca2+-binding domain. The domain is an open cavity in the first substate and can bind only a single Ca2+ ion. A fast "jaw-closing" (or "hinge-bending") step then partially closes the cavity to generate the second substate that has a second Ca2+-binding site. Occupation of this site is followed by another jaw-closing step that closes the binding cavity and occludes the bound ions. The subsequent translocation step (to form E2) remains unchanged from previous models. The modified model predicts a constant transport stoichiometry of two Ca2+ per pump reaction cycle. It suggests a plausible mechanism for coupling between Ca2+ binding and ATP utilization: the model predicts (in agreement with experiment) that Ca2+ binding should be a mandatory requirement for phosphorylation of the pump protein, though ATP binding per se does not require Ca2+. The model is consistent with high cooperativity in equilibrium binding of Ca2+, both in the absence and presence of ATP.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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