title: Cooperative effects of calcium on myofibrillar ATPase of normal and hypertrophied heart.
abstract: The ATPase of myofibrils from normal and hypertrophied rat heart was studied in relation to the Ca2+-dependence of the reaction. The experimental data were fitted to theoretical curves based on the Hill equation. A positive cooperativity (n = 1.6) was found for the activation curve of the ATPase from normal heart. For hypertrophied heart no significant change in either the cooperativity or the Ca2+-sensitivity of troponin was detected. This indicates that the troponin-tropomyosin system is not altered during pressure-overload hypertrophy. However, it should be noted that no precautions were taken to control the state of phosphorylation of contractile proteins during the preparation of myofibrils.
mesh_terms: D000251:Adenosine Triphosphatases; D000818:Animals; D002118:Calcium / Q000502:physiology*; D006332:Cardiomegaly / Q000201:enzymology*; D008274:Magnesium / Q000502:physiology; D008297:Male; D009206:Myocardium / Q000201:enzymology; D009210:Myofibrils / Q000201:enzymology*; D010085:Oxidative Phosphorylation; D051381:Rats; D014335:Tropomyosin / Q000502:physiology; D014336:Troponin / Q000502:physiology
chemical_list: D014335:Tropomyosin; D014336:Troponin; D000251:Adenosine Triphosphatases; D008274:Magnesium; D002118:Calcium