title: Conformational changes induced in plasmodium actin polymer by Ca2+ in the presence of muscle native tropomysin.
abstract: The flexible polymer of plasmodium actin (Mg-polymer) combines with muscle native tropomyosin up to a weight ratio of actin: tropomyosin:troponin = 6:1:1. Mg-polymer which combined with muscle native tropomyosin undergoes a conformational change when the Ca2+ concentration of the solution is decreased by adding 0.5 mM ethylene glycol bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA): the viscosity of the solution increases by 50% and its ATPase activity decreases to about 20% of the original value, which suggests that the structure of Mg-polymer becomes more rigid. This change is reversible with respect to the Ca2+ concentration in the solution. The threshold concentration of Ca2+ for the conformational change is about 10(-6) M. The possible role of this transformation in vivo is discussed.
mesh_terms: D000199:Actins; D000818:Animals; D001665:Binding Sites; D002118:Calcium; D007700:Kinetics; D046911:Macromolecular Substances; D009132:Muscles; D010804:Physarum; D011485:Protein Binding; D011487:Protein Conformation; D014335:Tropomyosin; D014783:Viscosity
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D014335:Tropomyosin; D002118:Calcium