The effects of platelet tropomyosin on the ATPase activities of muscle actomyosin subfragment 1 in the absence and presence of troponin, its components, and calmodulin.
The effect of platelet tropomyosin on the ATPase activity of a muscle actin-myosin subfragment 1 system has been examined in 30 mM KCl, 5 mM MgCl2, 2 mM ATP, 0.1 mM EGTA, 2 mM Tris, pH 7.8. Whereas muscle tropomyosin inhibits the activity by 60%, the platelet protein had no effect. Addition of muscle troponin in the absence of Ca2+ to the system inhibited the activity by up to 80% irrespective of whether muscle or platelet tropomyosin was used. The release of this inhibition by the addition of Ca2+ was much less in the case of platelet tropomyosin. This may result from the fact that platelet tropomyosin aggregates poorly in a head-to-tail manner and interacts only weakly with muscle troponin-T. In the presence of troponin-I and platelet tropomyosin, inhibition of the ATPase activity was 80%. This inhibition was largely released by the addition of troponin-C irrespective of the presence of Ca2+. The addition of brain calmodulin, however, released the inhibition in the presence of calcium but not in its absence. These effects can be correlated with the binding or lack of binding of the platelet tropomyosin to the actin filament.
D000199:Actins / Q000502:physiology*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D007700:Kinetics; D009124:Muscle Proteins / Q000502:physiology*; D009132:Muscles / Q000201:enzymology*; D015879:Myosin Subfragments; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D011817:Rabbits; D014335:Tropomyosin / Q000097:blood*; D014336:Troponin / Q000502:physiology*
D000199:Actins; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D009124:Muscle Proteins; D015879:Myosin Subfragments; D010446:Peptide Fragments; D014335:Tropomyosin; D014336:Troponin; D000251:Adenosine Triphosphatases; D009218:Myosins; D002118:Calcium