Actin filament annealing in the presence of ATP and phalloidin.

The re-formation of actin filaments after fragmentation by sonication in the presence of phalloidin and ATP has been found to follow second-order kinetics. The data are described by a model in which the rate of actin filament annealing is proportional to the square of the number concentration of actin filaments and the rate of fragmentation is proportional to the actin polymer concentration. In the presence of 100 mM KCl, 1 mM MgCl2, and equimolar phalloidin, the second-order rate constant for annealing of actin filaments is 2.2 x 10(6) M-1 s-1 and the first-order rate constant for fragmentation is 7 x 10(-7) s-1. In addition, the observed pseudo-first-order rate constant for annealing was found to increase with increasing ionic strength. Thus, annealing may play a major part in the length redistribution phase of actin polymerization and may be important for actin filament rearrangement in the cell.