tropomyosin A protein found in the actin filaments in muscles. The molecule consists of two elongated strands that run along the length of the filament. When the muscle is at rest, the tropomyosin molecule covers the binding site of the actin molecule, where interaction with myosin occurs. On contraction of the muscle, the tropomyosin is displaced by another protein, troponin, allowing the interaction of actin with myosin. See sliding filament theory.

tropomyosin A highly elongated protein, of relative molecular mass 70 000, that is composed of two alpha-helix subunits wound about each other. It is associated in vivo with actin and troponin in the thin filaments of striated muscle and inhibits the contraction of striated muscles when no calcium is present.