THE EXCHANGE OF CA2-RECEPTIVE PROTEIN COMPLEX (TROPONIN) IN THE MYOFIBRILS OF FAST AND SLOW SKELETAL-MUSCLES()

In order to compare the role of the Ca2+-receptive protein (troponin), in the characteristic myofibrillar contractile response of chicken fa st and slow skeletal muscles, the troponin in both kinds of myofibrils were partially exchanged, under slightly acidic conditions. The Ca2+- or Sr2+-activation of the ATPase of fast (or slow) skeletal myofibril s hybridized with slow (or fast) skeletal troponin profiles were also investigated. The results indicated that the Ca2+- or Sr2+-affinity of the myofibrillar ATPase activity were related to the species of tropo nin. This procedure for replacing troponin in myofibrils under physiol ogical conditions is thus considered to be useful for the study of the Ca2+-regulatory mechanism in myofibrillar contraction.