Tropomyosin as a regulator of the sliding movement of actin filaments.

We examined the capacity of tropomyosin molecules regulating the sliding movement of actin filaments on myosin molecules in the presence of ATP molecules to be hydrolyzed. For this objective, we prepared tropomyosin molecules modified to be a little bit stiffer compared to the intact ones by applying a fixed cross-linker between a pair of twisted tropomyosin monomers. The cross-linked tropomyosin molecules, when complexed with actin filaments, were found to inhibit the sliding movement of the filaments on myosin molecules even in the absence of calcium-regulated troponin molecules. It is then suggested that the mechanical flexibility of tropomyosin molecules may be instrumental to actualizing the proper functional regulation of the sliding movement of actin filaments.