title: Molecular and biological studies on cardiac muscle calcium-binding protein (TN-C).
abstract: TN-C was purified from bovine cardiac muscle. In the absence of Ca-2+, cardiac TN-C has an intrinsic sedimentation coefficient of 1.93 S and a molecular weight of 18 000 daltons. Cardiac TN-C reverses the inhibitory effect of skeletal TN-I on the Mg-2+-activated ATPase of a skeletal synthetic actomyosin preparation in the presence of skeletal tropomyoson. Circular dichroism (CD) studies indicate that cardiac TN-C undergoes a major conformational change upon binding Ca-2+. A similar response is elicited by Sr-2+, whereas Mg-2+ has a much less pronounced effect. The presence of Mg-2+ does not alter the net effects of either Ca-2+ or Sr-2+. Cardiac TN-C is rich in acidic amino acid residues. UV absorption, near UV CD, and fluorimetric studies show that the protein lacks tryptophan and has a relatively high phenylalanine to tyrosine ratio. The results of this study invite direct comparisons with results reported for the skeletal muscle analogue of cardiac TN-C.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002852:Chromatography, Ion Exchange; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009124:Muscle Proteins / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D011487:Protein Conformation; D011955:Receptors, Drug; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000596:Amino Acids; D009124:Muscle Proteins; D011955:Receptors, Drug; D000251:Adenosine Triphosphatases; D008274:Magnesium; D002118:Calcium