Effect of cofilin and Arp2/3 concentrations on pushing barbed end generation. (A) Increasing cofilin concentration leads to a cooperative increase in severing rate, , and (B) subsequently, an increase in pushing barbed end production. (C) Increasing Arp2/3 concentration, however, does not lead to a cooperative increase in nucleation rate, , and (D) the impact of Arp2/3 concentration on pushing barbed end concentration is negligible, noted by all lines collapsing on to one another.