title: Cooperative binding of tropomyosin to muscle and Acanthamoeba actin.
abstract: Analyses of the binding of tropomyosin to muscle and Acanthamoeba actin by the use of Scatchard plots indicate that the binding exhibits strong positive cooperativity in the presence of Mg2+. The cooperative nature of the binding is not affected by the presence of 80 mm KCl, but appears to decrease somewhat in the presence of heavy meromyosin or subfragment-1. Heavy meromyosin, subfragment-1, and KCl each increase the binding affinity of actin for tropomyosin; depending on the experimental condition and the type of actin involved, the apparent binding constant, Kapp, is in the range of 1 to 4 x 10(6) M-1. Muscle actin cross-linked with glutaraldehyde failed to bind tropomyosin even when heavy meromyosin, subfragment-1, or KCl were added as inducers, although the cross-linked actin still markedly activated the heavy meromyosin ATPase.
mesh_terms: D000199:Actins / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000656:Amoeba / Q000378:metabolism*; D000818:Animals; D007700:Kinetics; D046911:Macromolecular Substances; D009132:Muscles / Q000378:metabolism*; D015879:Myosin Subfragments / Q000378:metabolism; D011485:Protein Binding; D011817:Rabbits; D014335:Tropomyosin / Q000378:metabolism
chemical_list: D000199:Actins; D046911:Macromolecular Substances; D015879:Myosin Subfragments; D014335:Tropomyosin; D000251:Adenosine Triphosphatases