[Tropomyosin from smooth and skeletal muscles initiates various conformational changes in skeletal F-actin].

Changes in F-actin conformation in myosin-free single ghost fibers of rabbit skeletal muscle induced by the binding of skeletal and gizzard tropomyosin to F-actin were studied by measuring intrinsic tryptophan-polarized fluorescence of F-actin. It was found that skeletal and gizzard tropomyosin binding to F-actin initiate different conformational changes in actin filaments. Skeletal tropomyosin inhibits, while gizzard tropomyosin activates the Mg2+-ATPase activity of skeletal actomyosin. It is supposed that in muscle fibers tropomyosin modulates the ATPase activity of actomyosin via conformational changes in F-actin.