DECORATING ACTIN-FILAMENTS WITH TROPONIN T-I COMPLEXES AND ACCELERATION OF THEIR SLIDING MOVEMENT ON MYOSIN MOLECULES

Actin filaments, when partially decorated with troponin T-I complexes, can slide faster on myosin heads than those with no decoration. Purif ied troponin T-I complexes bind to actins, and inhibit the actin activ ated myosin adenosine 5'-triphosphatase activity completely when the m olar ratio of troponin T-I complex to actin is increased to 1 to 1. Th ose actin filaments decorated with troponin T-I complexes up to 20 to 50% of their molar ratio exhibit enhancement of the velocity of slidin g on myosins up to 20% compared to those without such decoration. As t he molar ratio of decoration further increases, the sliding velocity d ecreases. These results are consistent with the observation that even if some of actin monomers do not participate in the ATPase activity di rectly, they can interact with myosin heads and take part in the slidi ng movement.