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  • Title: Sodium-23 nuclear magnetic resonance as an indicator of sodium binding to troponin C and tryptic fragments, in relation to calcium content and attendant conformational changes.
    Author: Delville A, Grandjean J, Laszlo P, Gerday C, Grabarek Z, Drabikowski W.
    Journal: Eur J Biochem; 1980 Apr; 105(2):289-95. PubMed ID: 7379787.
    Abstract:
    The relaxation rate enhancements of the 23Na nuclei for NaHCO3 solutions of troponin C and its tryptic peptides TR-1 and TR-2 indicate true binding of Na+ ions to these biomolecules. The low-affinity sites I and II of TR-1 and troponin C are the sites of competitive Na+/Ca2+ binding, below one calcium ion per molecule, with log KNa approximately 2. At low calcium content Na+ ions bind to TR-2 and to troponin C non-competitively with Ca2+ ions; binding of Ca2+ ions to the high-affinity sites III and IV allosterically affects the binding of the Na+ ions: even when sites I and II, located on TR-1 or sites I, II, III, IV of troponin C, are saturated with Ca2+ ions, Na+ ions continue to bind weakly at secondary binding sites.
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