Calcium regulates troponin-tropomyosin binding in the reconstituted thin filament.
Steady-state fluorescence anisotropy technique was used to determine the binding constant of troponin for IAEDANS-labeled tropomyosin under various conditions. In the absence of actin, Ca does not affect the binding between troponin and tropomyosin. The presence of actin greatly strengthens troponin-tropomyosin binding in the absence of Ca. However, Ca weakens troponin-tropomyosin binding by about 2.5-fold in the reconstituted filament. It is suggested that the Ca-regulated binding may serve as a molecular switch for the troponin molecule to get "on" and "off" the actin-myosin interaction site regulating muscle contraction-relaxation cycles.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D007700:Kinetics; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism; D009282:Naphthalenesulfonates; D011485:Protein Binding; D011817:Rabbits; D014335:Tropomyosin / Q000378:metabolism*; D014336:Troponin / Q000378:metabolism*
D005456:Fluorescent Dyes; D009124:Muscle Proteins; D009282:Naphthalenesulfonates; D014335:Tropomyosin; D014336:Troponin; D004533:Egtazic Acid; C006421:1,5-I-AEDANS; D002118:Calcium