Fig. 5.

The steady-state occupancy of actin-binding sites on the membrane surface depends on the rates at which they are loaded and depleted. The WH2 and proline-rich domains are loaded by the binding of soluble actin monomers or profilin-actin complexes (left). These sites are depleted primarily by interactions between the bound actin and growing filament ends close to the membrane (right). Loading depends primarily on the concentration of soluble actin and profilin-actin, while depletion is proportional to the number of growing filament ends in proximity to the membrane. By capping fast-growing barbed ends, capping protein lowers the rate of depletion and increases the steady-state occupancy of surface actin pool