title: Interaction of calmodulin with troponin I and the troponin-tropomyosin-actin complex. Effect of Ca2+ and Sr2+ ions.
abstract: In an effort to elucidate the mechanism of calmodulin regulation of muscle contraction, we investigated the interaction between calmodulin and troponin components in the presence of Ca2+ or Sr2+ by the use of ultracentrifugation methods and polyacrylamide-gel electrophoresis. Skeletal-muscle troponin C bound to troponin I and dissociated it from the tropomyosin-actin complex in the presence of Ca2+ or Sr2+. When troponin T was absent, calmodulin bound to troponin I and dissociated it from the tropomyosin-actin complex in the presence of Ca2+ or Sr2+. When troponin T was present, calmodulin hardly bound to troponin I even in the presence of bivalent cations. Trifluoperazine, a calmodulin antagonist, inhibited the bivalent-cation-dependent interaction between calmodulin and troponin I. Calmodulin migrated more slowly in the presence of Sr2+ than it did in the presence of EGTA but faster than it did in the presence of Ca2+ on polyacrylamide-gel electrophoresis under non-denaturing conditions. It is concluded that troponin T is not required in the calmodulin regulation of muscle contraction because troponin T inhibits the bivalent-cation-dependent interaction between calmodulin and troponin I and because calmodulin binds to troponin I and dissociates it from the tropomyosin-actin complex in a bivalent-cation-dependent manner. Sr2+-induced exposure of the hydrophobic region enables calmodulin to bind to troponin I, as is the case with Ca2+.
mesh_terms: D000199:Actins / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D046911:Macromolecular Substances; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D013324:Strontium / Q000494:pharmacology*; D014268:Trifluoperazine / Q000494:pharmacology; D014335:Tropomyosin / Q000378:metabolism; D014336:Troponin / Q000378:metabolism*; D019210:Troponin I
chemical_list: D000199:Actins; D002147:Calmodulin; D046911:Macromolecular Substances; D014335:Tropomyosin; D014336:Troponin; D019210:Troponin I; C042260:troponin-tropomyosin complex; D014268:Trifluoperazine; D012967:Sodium Dodecyl Sulfate; D002118:Calcium; D013324:Strontium