{'fraction_non_alphanumeric': 0.03749098774333093, 'fraction_numerical': 0.010814708002883922, 'mean_word_length': 5.337899543378995, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Stoichiometry of calcium binding to a synthetic heterodimeric troponin‐C domain

In this work we describe calcium binding to two synthetic 34‐residue peptides, determined by 1H‐nmr spectroscopy. The peptides investigated, SCIII and SCIV, encompass the calcium‐binding sites III and IV, respectively, of troponin‐C. In the absence of calcium it has previously been shown that each of these peptides possesses little regular secondary structure. Further, the 1H‐nmr spectra of an equimolar mixture of both of these apo‐peptides (apo‐SCIII/SCIV) shows that little interaction occurs between peptides. Upon calcium binding the spectral changes that occur to SCIII/SCIV are consistent with global conformational changes in both peptides. We have shown previously that these conformational changes are a product of calcium binding to SCIII and SCIV to form a two‐site heterodimer Ca2‐SCIII/SCIV. It is proposed that this calcium‐induced folding proceeds via calcium binding to SCIII to form Ca‐SCIII, peptide association with apo‐SCIV to form the heterodimer Ca‐SCIII/SCIV, and calcium binding to form Ca2‐SCIII/SCIV. The dissociation constants involved in this pathway, K1, Kd, and K2, respectively, have been determined by stoichiometric calcium titration of SCIII/SCIV, monitored by 1H‐nmr spectroscopy. Using this procedure it has been determined that K1 = 3 μM, Kd = 10 μM, and K2 = 2 μM.