Effect of cytochalasin B on formation and properties of muscle F-actin

Cytochalasin B stimulated polymerization and decreased the concentration of G-actin remaining in equilibrium with F-actin filaments. Polymerization in the presence of cytochalasin B gave rise to a smaller increase of viscosity but to the same increase in light scattering, compared to polymerization in the absence of cytochalasin B. Cytochalasin B reduced the viscosity of F-actin and caused the appearance of ATP hydrolysis by F-actin. The cytochalasin B-induced ATPase activity was inhibited by concentrations of KCl higher than 50 mM. The cytochalasin B-induced ATPase activity was enhanced by ethyleneglycol bis(α-aminoethyl ether)-N,N′-tetraacetic acid and reduced by MgCl₂ at concentrations higher than 0.75 mM. The findings suggest that the stability of actin filaments is reduced by cytochalasin B.