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Delville, A; Brandjean, J; Laszlo, P; Gerday, C; Grabarek, Z; Drabikowski, W. (Liege Univ. (Belgium). Inst. de Chimie Organique et de Biochemie. Lab. de Chimie Organique Physique)
European journal of biochemistry, April 1980, Letnik: 105, Številka: 2Journal Article
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∼ 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.
