Troponin-tropomyosin interactions. Fluorescence studies of the binding of troponin, troponin T, and chymotryptic troponin T fragments to specifically labeled tropomyosin.

We have studied the interaction between troponin and tropomyosin by means of a fluorescent probe, N-(1- anilinonaphth -4-yl)maleimide (ANM), attached to the cysteine-190 residues of tropomyosin. The binding of troponin and troponin T to ANM-tropomyosin produces substantial increases in the label fluorescence. Analysis of the binding profiles indicates that both troponin and troponin T bind with a 1:1 stoichiometry. We have obtained and characterized several chymotryptic fragments of troponin T by digestion of isolated troponin T or whole troponin. An N-terminal fragment from troponin T which is slightly less than two-thirds of the whole molecule binds to tropomyosin without affecting the label fluorescence; a C-terminal fragment composed of the rest of the troponin T molecule causes a substantial enhancement of the label fluorescence. We have also isolated a complex containing the C-terminal troponin T fragment together with troponin I and troponin C from whole troponin, which also enhanced the label fluorescence. These observations indicate an elongated region of attachment between troponin T and tropomyosin.