Interaction of calmodulin with the particulate fraction of cardiac muscle.
Tritiated calmodulin (T-CM) was bound to the EGTA-treated particulate fraction of cardiac muscle in a calcium-dependent manner with half-maximal binding occurring between 0.8 to 1.2 microM calcium. Binding exhibited high specificity at an optimum pH of 7.4-7.6. An excess of parvalbumin and other globular proteins did not displace T-CM. The Kd for the interaction was 2.5 +/- 0.83 microM. Binding was trypsin-sensitive, inhibited by high ionic strength and was heat inactivated at a midpoint of 48 - 50 degrees C. Competitive displacement of T-CM occurred with unlabeled troponin C and calmodulin over the same concentration range. The first-order rate constant of T-CM dissociation was 3.27 min-1. Calcium-dependent binding of T-CM was inhibited equally by both mepacrine and trifluoperazine with 50 percent inhibition occurring at 70 microM.
D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D006352:Heart Ventricles / Q000378:metabolism; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D011506:Proteins / Q000494:pharmacology; D051381:Rats
D002147:Calmodulin; D011506:Proteins; D004533:Egtazic Acid; D002118:Calcium