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. 1999 Apr 15;339(Pt 2):351–357.

Luminal dissociation of Ca2+ from the phosphorylated Ca2+-ATPase is sequential and gated by Mg2+.

R C Duggleby 1, M East 1, A G Lee 1
PMCID: PMC1220164  PMID: 10191266

Abstract

Transport of Ca2+ across the membrane by the Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum involves the transfer of two Ca2+ ions from a pair of cytoplasmic sites to a pair of luminal sites, driven by phosphorylation of the ATPase. The ATPase is inhibited by Mg2+ at alkaline pH values. Inhibition follows from a decrease in the rate of release of Ca2+ from the phosphorylated ATPase. Phosphorylation-induced release of Ca2+ from the ATPase is biphasic at alkaline pH, which is consistent with sequential release of Ca2+ from the phosphorylated ATPase; the rates of both components decrease with increasing Mg concentration. The effect of Mg2+ on the slow phase of release follows from the binding of Mg2+ at the empty outer luminal site, vacated by the release of the first Ca2+ ion. The effect of Mg2+ on the rate of release of the first Ca2+ ion could follow from binding to a gating site also affecting the binding of Ca2+ to the cytoplasmic sites.

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Selected References

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