Occluded bound calcium on the phosphorylated sarcoplasmic transport ATPase

Takisawa, H.; Makinose, Madoka

doi:10.1038/290271a0

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Occluded bound calcium on the phosphorylated sarcoplasmic transport ATPase

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Takisawa, H.
Max Planck Institute for Medical Research, Max Planck Society;

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Makinose, Madoka
Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Takisawa, H., & Makinose, M. (1981). Occluded bound calcium on the phosphorylated sarcoplasmic transport ATPase. Nature, 290(5803), 271-273. doi:10.1038/290271a0.

Cite as: https://hdl.handle.net/21.11116/0000-0005-0CD7-C

Abstract

The Ca2+ + Mg2+-activated ATPase of the sarcoplasmic reticulum is responsible for the active Ca2+ transport of this membrane system, the key feature of which is the formation of an energy-rich phosphorylated transport enzyme (EP) and its conversion. To understand the Ca2+-transport mechanism, it is essential to clarify the behaviour of this intermediate in relation to such ligands as ATP, ADP, Mg2+ and, particularly, Ca2+. Recent kinetic studies on the phosphate turnover of this system suggested a relatively slow rate of Ca2+ dissociation from the phosphorylated enzyme, which possibly indicated Ca2+ binding in some occluded form with the intermediate. Here we report direct measurements of the binding and release of Ca2+ during phosphorylation of the sarcoplasmic transport enzyme. The results indicate an occlusion of the Ca2+ binding, accompanying an initial configurational change of the enzyme induced by the energy-rich phosphoryl transfer.