title: The interaction of equine platelet tropomyosin with skeletal muscle actin.
abstract: Whereas skeletal muscle tropomyosin binds strongly to muscle F-actin in a buffer containing 30 mM KCl and 1-2 mM free Mg2+, equine platelet tropomyosin only binds stoichiometrically (1 tropomyosin molecule per 6 actin monomers) at higher Mg2+ concentrations (7-8 mM free Mg2+). At low free Mg2+ concentrations (1.5 mM) the binding of the platelet protein is only marginally increased by raising the KCl concentration to an optimal value (0.10-0.20 M). This weaker binding can be attributed to the relatively poor head-to-tail polymerization of platelet tropomyosin and its fewer actin-binding sites. In a buffer containing 30 mM KCl and 3 mM Mg2+, the binding of platelet tropomyosin to F-actin can be induced by the addition of either skeletal muscle myosin subfragment 1 or troponin-I. The binding induced by troponin-I is largely neutralized by the addition of troponin-C both in the presence and absence of Ca2+, but by calmodulin only in the presence of Ca2+.
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D006736:Horses; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011485:Protein Binding; D011817:Rabbits; D014335:Tropomyosin / Q000097:blood*
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D014335:Tropomyosin; D011189:Potassium Chloride; D008274:Magnesium