Figure 2.

Three methods of fitting simulations of the nucleation model to the time courses of spontaneous polymerization of three concentrations of 7.5% pyrenyl-Mg-ATP-actin monomers. Symbols are the experimental measurements of the polymer concentration or calculated concentrations of monomers and filament ends. Smooth curves are numerical simulations of the model constrained by time courses of (column 1) the concentration of polymerized actin measured from the pyrene fluorescence for polymer, (column 2) polymer and filament end concentration calculated at each time point from the rate of polymerization and the actin monomer concentration, and (column 3) polymer, monomer (calculated at each time point from the concentration of total actin minus the polymer concentration), and filament end concentrations. Shown are (row 1) concentration of polymer versus time, (row 2) concentration of actin monomer versus time, and (row 3) concentration of filament ends versus time. Concentration of actin monomer was only used to constrain column 3. Concentration of filament ends versus time was only used to constrain columns 2 and 3. Shown in row 4, PLEs of the actin nucleation parameters for the three methods to constrain the fits. Symbols correspond to the RSS from best-fit values for each fixed value of the rate constant plotted on the x axis. The red line indicates the 95% CI. The two intersections of the curves give the range in which each parameter is identifiable. To see the figure in color, go online.