The binding of skeletal muscle C-protein to regulated actin

The binding of C-protein, a component of thick filament of myofibrils, to regulated actin filaments in the presence or absence of Ca2+ was studied. The amount of C-protein bound to regulated actin filaments in the presence of Ca2+ was higher than those in the absence of Ca2+. The addition of C-protein to regulated actin caused an increase in turbidity, especially in the presence of Ca2+, and this was found to result from side-by-side association of actin filaments into bundles. In the absence of Ca2+, no actin filament bundles were formed.