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 fast 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 myofibrils 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 troponin. This procedure for replacing troponin in myofibrils under physiological conditions is thus considered to be useful for the study of the Ca2+-regulatory mechanism in myofibrillar contraction.