The effect of troponin C removal on the Ca2+-sensitive binding of Mg2+AMPPNP to myofibrils

Abstract It was previously shown that when rabbit skeletal myofibrils are titrated with Mg 2+ AMPPNP under conditions that result in the dissociation of cross-bridges from the thin filaments (i.e. 50% ethylene glycol, O°C), Ca 2+ -sensitive, biphasic binding is observed. These titrations have been repeated using myofibrils from which the troponin C has been selectively removed. The disappearance of both Ca 2+ sensitivity and biphasic binding is taken as evidence that the Ca 2+ sensitivity is due to Ca 2+ binding to troponin C and the biphasic binding of Mg 2+ AMPPNP observed in intact myofibrils is not due to packing constraints or steric hindrance.