Kinetics of Ca2+ release shows interactions between the two classes of sites of troponin-C.
The kinetics of Ca2+-release from the two high affinity sites of troponin-C (TnC) was studied by the stopped flow technique following rapid mixing with either EDTA or excess TbCl3. The rate constants obtained by the two methods were 2.8 and 0.7 s-1, respectively. For the tryptic fragment of TnC that contains only the COOH-terminal half of the molecule, both methods generate rate constants of 2.2 s-1. These results are consistent with the interpretation that binding of Tb3+ to the Ca2+-specific sites reduces the rate of dissociation of Ca2+ from, and thereby enhances the affinity for, the Ca2+-Mg2+ sites; this, in turn, suggests interactions between the two halves of the TnC molecule.
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D009124:Muscle Proteins / Q000378:metabolism*; D011817:Rabbits; D013725:Terbium / Q000378:metabolism; D014336:Troponin / Q000378:metabolism*; D019209:Troponin C; D014357:Trypsin / Q000378:metabolism
D009124:Muscle Proteins; D014336:Troponin; D019209:Troponin C; D013725:Terbium; D004492:Edetic Acid; D014357:Trypsin; D008274:Magnesium; D002118:Calcium