Phalloidin (2 mol per mol actin)-treated pyrenyl F-actin showed a critical concentration of 1.8 μM in the presence of 10 mM KCl, 0.2 mM ADP, and 5 mM Tris-HCl buffer, pH 8.0 at 25°C. The filament weight concentration did not change at all during and after sonication, yet degrees of flow birefringence increased and the filament number concentration decreased after the termination of sonication. The latter changes were not affected by EDTA, but inhibited by β-actinin. These observations suggest that reannealing of short pieces of phalloidin-treated actin filaments fragmented during sonication takes place during recovery after sonication.
