(troe poe my´ oh sin) • A protein that, along with actin, constitutes the thin filaments of myofibrils. It controls the interactions of actin and myosin necessary for muscle contraction.

A protein associated with the thin filaments of striated muscle cells. Tropomyosin controls the access of myosin to the myosin binding site of actin.

A protein on thin filaments that covers the active sites in the absence of free calcium ions.