These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Lumenal Ca2+ dissociation from the phosphorylated Ca(2+)-ATPase of the sarcoplasmic reticulum is sequential.
    Author: Forge V, Mintz E, Canet D, Guillain F.
    Journal: J Biol Chem; 1995 Aug 04; 270(31):18271-6. PubMed ID: 7629146.
    Abstract:
    Once two radioactive Ca2+ coming from the cytoplasm are bound to the transport sites of the nonphosphorylated ATPase, excess EGTA induces rapid dissociation of both ions, whereas excess nonradioactive Ca2+ only reaches one of the two bound Ca2+. This difference has been explained assuming that the two Ca2+ sites are in a single file channel in which the superficial Ca2+ is freely exchangeable from the cytoplasm, whereas the deeper Ca2+ is exchangeable only when the superficial site is vacant. The same experiment was done using phosphorylated ATPase to determine whether Ca2+ dissociation toward the lumen is sequential as well. Under conditions that allow ADP-sensitive phosphoenzyme to accumulate (leaky vesicles, 5 degrees C, pH 8, 300 mM KC1), we found the same two pools of Ca2+. Excess EGTA induced dissociation of both ions together with dephosphorylation. Excess nonradioactive Ca2+ induced the exchange of half the radioactive Ca2+ without any effect on the phosphoenzyme level. Our results show a close similarity between the transport sites of the nonphosphorylated and the phosphorylated enzymes, although the orientation, affinities, and dissociation rate constants are different.
    [Abstract] [Full Text] [Related] [New Search]