The effect of partial removal of troponin I and C on the Ca(2+)-sensitive ATPase activity of rabbit skeletal myofibrils.

The effect of partial removal of troponin I and C on the profiles of Ca(2+)-sensitive ATPase activity in rabbit skeletal myofibrils was investigated by replacing the troponin C.I.T-complex in the myofibrils with exogenously added troponin T under the same conditions as those reported previously [Shiraishi et al. (1992) J. Biochem. 111, 61-65]. During the course of the troponin T treatment, the level of the ATP hydrolysis at low Ca2+ concentrations was elevated and the pCa for half maximum activation increased, while the cooperativity decreased. These changes in the parameters of the ATPase were correlated with the extent of the troponin I removal from myofibrils.