The exchange of Ca(2+)-receptive protein complex (troponin) in the myofibrils of fast and slow skeletal muscles.

In order to compare the role of the Ca(2+)-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 Ca(2+)- or Sr(2+)-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 Ca(2+)- or Sr(2+)-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 Ca(2+)-regulatory mechanism in myofibrillar contraction.