Troponin is composed of an activating factor, troponin C, and an inhibitory factor, troponin I. There is also a third factor, which binds to tropomyosin called troponin T. Troponin T is a single peptide of 259 (mostly charged) residues. This highly charged molecule is insoluble, unless in high ionic strength conditions. Troponin T binds to actin and troponin I forming a complex that moves the tropomyosin molecule.
Troponin T is part of the troponin-linked calcium regulation system which ultimately controls muscle contraction. In order for Ca2+ sensitive contraction to occur, this requires a Ca2+ receptive protein; troponin. Ca2+ action on troponin activates contraction within the muscle. Troponin T regulates the function of the troponin complex as it retains the Ca2+ regulating ability. Troponin T makes the neutralising action of Troponin C become sensitive to concentrations of Ca2+ .