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Old 05-17-2011
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Question What exactly does Troponin I do?

BRS physiology (5th edition) page 17 says this:

"Troponin I ("I" for inhibition) inhibits the interaction of actin and myosin"

... Isn't that the role of tropomyosin? I would imagine troponin I would do a poor job of inhibiting actin-myosin interaction, considering you only have one troponin complex for every 7 actin binding sites.

Wikipedia appears to describe troponin I as being the component of the troponin complex that actually connects the troponin-tropomyosin complex to actin, however the article text is not written very clearly:

"Troponin I is a part of the troponin complex. It binds to actin in thin myofilaments to hold the actin-tropomyosin complex in place. Because of it myosin cannot bind actin in relaxed muscle. When calcium binds to the Troponin C it causes conformational changes which lead to dislocation of troponin I and finally tropomyosin leaves the binding site for myosin on actin leading to contraction of muscle. The letter I is given due to its inhibitory character."

What does it mean when it says calcium binding leads to "dislocation of troponin I?" And how does any of this relate to the protein's eponymous letter designation?

Thanks as always,
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Musculoskeletal-, Physiology-

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