Figure 5

Experimental and predicted values for actinnucleation. A to F. Effect of ATP and lipids. Phagosomal preparations were incubated with actin and 0.2 mM (red) or 5 mM (blue) ATP. The percentage of phagosomes nucleating actin was measured under control conditions (estimated initial lipid concentrations in "Phagosomal lipid assumptions", Methods) or after addition of a single lipid (estimated initial concentration in "Lipid incorporation into phagosomes", Methods). For all panels, the percentage of positive phagosomes was used to estimate the number of active sites polymerizing actin (n_aActin) and expressed in arbitrary units (AU). G. n_aActin was estimated when the assay was supplemented with different concentrations of ATP. Symbols in panels A to G: experimental n_aActin ± SEM (N = 3–5); the model predictions are shown as solid lines having the same colours than the corresponding experimental observations. H. Phagosomal preparations were incubated first with DAG and 0.2 mM ATP. After 5 min, PIP was added to the assay together with actin, and the percentage of phagosomes nucleating actin was measured. I. Same protocol as in H, except that PIP was added during the preincubation and DAG together with actin. In H and I, the predicted number of inactive sites (n_i, black lines), active sites (n_a, blue lines) and active sites nucleating actin (n_aActin, red lines) are shown together with the experimental values [n_aActin(e), red circles ± SEM, N = 3].