Comparative calcium binding and conformational studies of turkey and rabbit skeletal troponin C

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Abstract
Troponin C from turkey skeletal muscle has been compared with its chicken counterpart in terms of amino acid composition and fragmentation patterns and with rabbit TN-C by Ca 2+ binding and conformational response to Ca 2+ as monitored by CD and fluorescence. Cyanogen bromide and tryptic digestion mixtures of chicken and turkey TN-C have been separated by reversed-phase HPLC. The similarity of the elution profiles, along with the almost identical amino acid compositional data, suggest that the sequences are essentially equivalent. Both turkey and rabbit TN-C bound 2 mol Ca 2+ /mol protein at pH 5.3, while at pH 6.8, this figure was raised to 4 mol/mol protein. Circular dichroism and fluorescence measurements indicated that the conformations of the two proteins responded in a very similar manner to the presence of Ca 2+