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Is the ATP molecule which is bound to the myosin head for relaxation of the muscle (i.e., to break the cross bridge) also utilized for active transport of calcium to the sarcoplasmic reticulum during muscle relaxation?

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    $\begingroup$ ATP is used for ion pumps as well as movement of molecular motors. It is of course not the same molecule that does both simultaneously. How can it!! $\endgroup$
    – WYSIWYG
    Commented Dec 22, 2014 at 12:18
  • $\begingroup$ Thanks. ..I just read in a book , I got confused. ..thanks for clearing up the matter $\endgroup$ Commented Dec 22, 2014 at 13:25
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    $\begingroup$ @WYSIWYG: you have my deepest respect for understanding this question! I edited accordingly, thanks! Convert to an answer and you will get a much deserved +1 $\endgroup$
    – AliceD
    Commented Dec 22, 2014 at 13:33
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    $\begingroup$ Yeah I somewhat guessed the meaning. Tried some edits but I left it to the OP to explain the rest. $\endgroup$
    – WYSIWYG
    Commented Dec 22, 2014 at 13:46

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ATP is used (hydrolyzed) by ion pumps to transport ions such as calcium against their concentration gradient.

Molecular motors (such as myosin and kinesin) also couple ATP hydrolysis with movement.

However both these processes are separate and just because calcium flux changes happen during muscle contraction doesn't mean that it is the same ATP that drives some kind of a bifuntional enzyme to perform both tasks.

Moreover calcium is released during the contraction phase from the sarcoplasmic reticulum (SR); pumping back the calcium to the SR happens during the repolarization (there is no myosin movement at this stage).

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