Cytochalasin B-induced ATPase activity of actin: dependence on monomer concentration.

We simultaneously measured polymerization and ATPase activity of actin induced by cytochalasin B. It was found that under all conditions tested, ATPase activity was proportional to the concentration of actin which was unpolymerized. In addition, it was found that conditions increasing ATPase activity also increase the velocity of polymerization. From this we conclude that CB-induced ATPase activity is a property of the actin monomers and that the "readiness" of the monomers to hydrolyze ATP is correlated with an increased capacity of the monomers to polymerize.