title: The thin filament of vertebrate skeletal muscle co-operatively activates as a unit.
abstract: We find that extraction of as little as one troponin C molecule per troponin-tropomyosin strand on a thin filament reduces the slope of the pCa/tension relation. We interpret this to mean that the regulatory units along a thin filament of rabbit psoas fibers are linked co-operatively so that a thin filament activates as a unit. The presence of extended co-operativity explains why the pCa/tension relation in skinned fibers has a slope much higher than predicted by binding of Ca2+ to one regulatory unit. Replacement of the extracted troponin C with purified troponin C fully reverses the effect of extraction and shows it to be the essential Ca2+ binding protein responsible for the steep slope of the pCa/tension relation.
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D009119:Muscle Contraction; D009132:Muscles / Q000648:ultrastructure*; D011817:Rabbits; D014336:Troponin / Q000378:metabolism; D019209:Troponin C
chemical_list: D014336:Troponin; D019209:Troponin C; D002118:Calcium