Calcium binding to low-affinity sites on troponin C induces a conformational change in troponin T, providing insight into the molecular mechanics of muscle contraction.
Should not yet change clinical management of contractile disorders; leaves open troponin C site-specific targeting in future mechanistic studies.
The skeletal muscle troponin complex, the troponin T subunit of which was labeled with 2-((4'-iodoacetamido)anilino)naphthalene-6-sulfonic acid, showed a fluorescence titration curve with a midpoint of around pCa 6.75. Addition of 2 mM MgCl2 had no effect on the fluorescence titration curve. Therefore, we conclude that Ca2+ binding to the low affinity Ca2+-binding sites of troponin C induces a conformational change of troponin T, but Ca2+ binding to the high affinity Ca2+-binding sites does not.
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Takayoshi Iio (1985) studied this question.
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