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troponin

(Science: protein) complex of three proteins, Troponins C, I, & T, associated with tropomyosin and actin on the thin filament of striated muscle, upon which it confers calcium sensitivity. There is one troponin complex per tropomyosin. Troponin C (18 kD) binds calcium ions reversibly, has a variable number of eF hand motifs and is the least variable of the subunits. TnC binds TnI & tnT, but not actin. Troponin I (23 kD) binds to actin and at 1:1 stoichiometry can inhibit the actin myosin interaction on its own. Troponin T (37 kD) binds strongly to tropomyosin.