Proton magnetic resonance studies on proteolytic fragments of troponin-C. Structural homology with the native molecule.

Comparison of proton magnetic resonance spectra of a tryptic and a thrombin fragment of troponin-C with that of the native protein has identified the domain of the molecule influenced by Ca2+ binding to the lower affinity regions I and II of troponin-C. The binding of Ca2+ to these sites results in a subtle alteration of the tertiary fold of the N-terminal half of troponin-C involving weakened contacts between several hydrophobic groups. The role and kinetics of the movements within the troponin-C molecule associated with binding at the regulatory sites are discussed.