Calcium binding to troponin C as a primary step of the regulation of contraction. A microcalorimetric approach.
Microcalorimetric titration studies of EF-hand Ca-binding proteins (troponin C, calmodulin and parvalbumins) resulted in the notion that Ca binding to the "active" Ca site, which is involved in the regulation of contraction, induces a characteristic anomalous enthalpy and heat-capacity changes indicating an exposure of hydrophobic residues to the solvent, which enables the proteins to interact with their targets. There is a good agreement between the results of the calorimetric and the structural studies in frog and chicken skeletal troponin C. In both species one of the N-terminal low-affinity Ca-sites is the "active" Ca site regulating muscle contraction. The results from calorimetry have shown, however, that the situation in rabbit skeletal troponin C may be more complex. Moreover, in both calorimetric and structural studies, the situation in cardiac troponin C is quite different. These results suggest the need for further studies to elucidate the mechanism of regulation by Ca. These characteristic changes do not occur in Ca-buffering proteins.
Yamada
Kazuhiro
K
Department of Physiology, Oita Medical University, Oita 879-5593, Japan.
D008841:Actin Cytoskeleton / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry*; D002151:Calorimetry; D002417:Cattle; D002614:Chelating Agents / Q000494:pharmacology; D006358:Hot Temperature; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011817:Rabbits; D011898:Ranidae; D013696:Temperature; D013997:Time Factors; D019209:Troponin C / Q000737:chemistry* / Q000378:metabolism
D002614:Chelating Agents; D019209:Troponin C; D002118:Calcium