Effect of muscle tropomyosin on the kinetics of polymerization of muscle actin.
At saturating concentrations, tropomyosin inhibited the rate of spontaneous polymerization of ATP-actin and also inhibited by 40% the rates of association and dissociation of actin monomers to and from filaments. However, tropomyosin had no effect on the critical concentrations of ATP-actin or ADP-actin. The tropomyosin-troponin complex, with or without Ca2+, had a similar effect as tropomyosin alone on the rate of polymerization of ATP-actin. Although tropomyosin binds to F-actin and not to G-actin, the absence of an effect on the actin critical concentration is probably explicable in terms of the highly cooperative nature of the binding of tropomyosin to F-actin and its very low affinity for a single F-actin subunit relative to the affinity of one actin subunit for another in F-actin.
D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D046911:Macromolecular Substances; D009132:Muscles / Q000378:metabolism*; D011817:Rabbits; D014335:Tropomyosin / Q000378:metabolism*
D000199:Actins; D046911:Macromolecular Substances; D014335:Tropomyosin; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D002118:Calcium