In the presence of readily available ATP-G-actin cofilin speeds up actin polymerization via its actin-severing activity (providing free barbed ends for further polymerization and nucleation by the Arp2/3 complex). As a long-lasting "in vivo" effect, cofilin recycles older ADP-F-actin, helping cell to maintain ATP-G-actin pool for sustained motility. pH, phosphorylation and phosphoinositides regulate cofilin's binding and associating activity with actin  The Arp2/3 complex and cofilin work together to reorganize the actin filaments in the cytoskeleton. Arp 2/3, an actin binding proteins complex, binds to the side of ATP-F-actin near the growing barbed end of the filament, causing nucleation of a new F-actin branch, while cofilin-driven depolymerization takes place after dissociating from the Arp2/3 complex. They also work together to reorganize actin filaments in order to traffic more proteins by vesicle to continue the growth of filaments. Cofilin also binds with other proteins such as myosin, tropomyosin, α-actinin, gelsolin and scruin. These proteins compete with cofilin for actin binding. Сofilin also play role in innate immune response. ADF/cofilin is found in ruffling membranes and at the leading edge of mobile cells. In particular, ADF/cofilin promotes disassembly of the filament at the rear of the brush in "Xenopus laevis" lamellipodia, a protrusion from fibroblast cells characterized by actin networks. Subunits are added to barbed ends and lost from rear-facing pointed ends. Increasing the rate constant, k, for actin dissociation from the pointed ends was found to sever actin filaments. Through this experimentation, it was found that ATP or ADP-Pi are probably involved in binding to actin filaments.