The steady-state ATPase activity of sarcoplasmic-reticulum (Ca(2+)-Mg2+)-ATPase is inhibited by thapsigargin at a molar ratio of 1:1, with a dissociation constant for thapsigargin estimated to be in the sub-nanomolar range. In the presence of thapsigargin, only a single Ca2+ ion binds to the ATPase. Similarly, addition of thapsigargin to the ATPase incubated in the presence of Ca2+ results in the release of one of the two originally bound Ca2+ ions. As monitored by the fluorescence of nitrobenzo-2-oxa-1,3-diazole-labelled ATPase, thapsigargin appears to shift the transition between E1 and E2 conformations towards E2. Addition of thapsigargin prevents phosphorylation of the ATPase by P(i) and results in a very low steady-state level of phosphorylation of the ATPase by ATP, as observed previously for nonylphenol.
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Research Article| April 15 1992
Mechanism of inhibition of the calcium pump of sarcoplasmic reticulum by thapsigargin
A G Lee;
Biochem J (1992) 283 (2): 525–529.
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M Wictome, I Henderson, A G Lee, J M East; Mechanism of inhibition of the calcium pump of sarcoplasmic reticulum by thapsigargin. Biochem J 15 April 1992; 283 (2): 525–529. doi: https://doi.org/10.1042/bj2830525
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