Figure 8.

Synaptopodin 2 increases the critical concentration of actin. Two experiments are shown in the absence of fesselin (circles and squares) and two in the presence of fesselin (triangles). Varying concentrations of column purified G-actin, 20% pyrene-labeled, were mixed with avian fesselin, keeping the free fesselin concentration constant at either 0.01 μM (triangles up, θ = 0.018) or 0.007 μM (triangles down, θ = 0.013). The reaction conditions were 2 mM MgCl₂, 100 mM KCl, 1.5 mM imidazole pH 7.0, 3.3 mM Tris pH 8.0, 0.066 mM CaCl₂, and 1 mM dithiothreitol. The critical concentration for actin alone (circles and squares) was 0.26 μM). The critical concentration for actin in presence of fesselin (triangles) was between 0.43 and 0.46 μM.