Binding of Troponin Components to Tropomyosin Fragments

Binding abilities of troponin components to two fragments of rabbit skeletal alpha-tropomyosin, one the N-chain (residues 1-189) obtained by specific cleavage at Cys 190 and the other the p-fragment (residues 183-284) of the tryptic product, were investigated by gel electrophoresis. The mixture of the tropomyosin fragments showed a new band of complex with either troponin (T + C) or whole troponin, troponin-(T + I + C), irrespective of the presence of Ca2+ in solution. On the other hand, troponin-T and troponin-(T + I) as well as troponin-C, -I, and -(I + C) had little bindin capacity to the tropomyosin fragments. Thus, troponin-C enhances the binding capacity of troponin-T to tropomyosin fragments. A two-site binding of troponin-T to tropomyosin is proposed.