Fig. 8.

Polymerization kinetics and myosin ATPase activation of unphosphorylated actin and pY53-actin. (A) Four-micromolar pY53-actin was polymerized alone (control) or in the presence of 20 nM gelsolin or 30 nM Arp2/3-VCA. (B) Unphosphorylated actin (4 μM) polymerized alone or in the presence of 20 nM gelsolin or 30 nM Arp2/3-VCA. (C) Correlation between ATP hydrolysis (circles) and spectrin–actin- (1.3 nM) nucleated polymerization (triangles) of 7.6 μM unphosphorylated actin (filled symbols) and 7.6 μM pY53-actin (open symbols). (D) ATPase activity of 150 nM Dictyostelium myosin II S1 as a function of the concentration of unphosphorylated and pY53-phosphorylated actin.