The binding sites of rabbit skeletal troponin-I on troponin-T.

Various fragments derived from rabbit skeletal muscle troponin-T (Tn-T) by chemical and (or) proteolytic cleavage were mixed with whole troponin-I (Tn-I) and applied to Sephadex G-75 gel filtration column in order to determine the binding site of Tn-I on Tn-T. This site of interaction was found to span two distinct regions of Tn-T. The first site involves the highly acidic NH2-terminal fragment CB3 (residues 1-70 of Tn-T). A second separate site is located in the region of residues 152-209 of Tn-T. The present study, in conjunction with our earlier work on tropomyosin - Tn-T binding and Tn-T - troponin-C binding, depicts Tn-T as being a functionally efficient molecule composed of several distinct domains of specialized amino acid sequence, each of which carries out a role in the binding of a different protein.