Investigation of cation-binding properties of cardiac troponin C peptides by circular-dichroism spectroscopy.
Bovine cardiac troponin C was cleaved at residues cysteine-35 and cysteine-84. Three peptides, N-terminal (residues 1-34), central (residues 35-83) and C-terminal (residues 84-161), of cardiac troponin C were obtained in a homogeneous state. Saturation of troponin C or its C-terminal peptide with Ca2+ or Mg2+ is accompanied by an increase in the ellipticity at 222 nm in the c.d. spectrum. The half-maximal changes in the ellipticity of troponin C were observed at 32 nM-Ca2+ or 56 microM-Mg2+. The corresponding values for the C-terminal peptide are 7.1 nM for Ca2+ and 4.5 microM for Mg2+. The ellipticity of the central peptide (residues 35-83) containing the second cation-binding site was decreased on saturation with Ca2+. The half-maximal changes in the ellipticity occur at 80 microM-Ca2+. Study of the c.d. spectra suggests that the alpha-helices flanking the second cation-binding site of cardiac troponin C exist independently of Ca2+. Saturation of the third and fourth sites with these cations is associated with a considerable increase in the alpha-helix content, probably due to the formation of an alpha-helix flanking the third site on the N-terminus.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001665:Binding Sites; D002118:Calcium; D002417:Cattle; D002942:Circular Dichroism; D008274:Magnesium; D010446:Peptide Fragments / Q000302:isolation & purification; D011485:Protein Binding; D011487:Protein Conformation; D014336:Troponin; D019209:Troponin C
D000596:Amino Acids; D010446:Peptide Fragments; D014336:Troponin; D019209:Troponin C; D008274:Magnesium; D002118:Calcium