Actin filaments copolymerized with both intact and chemically modified
actin monomers restored their sliding activity when they were supplem
ented with tropomyosin extracted from skeletal muscle. In contrast, th
e ATPase activation of the copolymers was decreased when supplemented
with tropomyosin. The results indicate that tropomyosin along with act
in monomers may facilitate sliding activity of the entire actin filame
nt but suppress ATPase activation of intact actin monomers themselves.
Accordingly, tropomyosin molecules could be viewed as playing a dual
role of both mechanical and chemical regulation of actin monomers.