FIGURE 4:

Impact of changing the number of MT seeds in competing systems. Steady-state concentrations of free (squares) and polymerized (circles) tubulin in competing systems as in Figure 3, A and B. (A, C) Simplified model with MTs growing from 5, 100, or 500 stable MT seeds (data for 100 seeds replotted from Figure 3A). (B, D) Detailed model with MTs growing from 5, 40, or 100 stable MT seeds (data for 40 seeds replotted from Figure 3B). Panels C and D show zoom-ins on the data plotted in panels A and B, respectively. The darker curves with smaller symbols correspond to fewer seeds and the lighter curves with larger symbols correspond to more seeds. Interpretation: These data show that changing the number of stable MT seeds alters the approach to the asymptotes determining Q1 and Q2 (dashed gray lines replotted here from Figure 3, A and B), but does not change the value of Q1 ≈ Q2. Methods: Data points represent the mean ± one SD of the values obtained in three independent runs of the simulations. Similar to Figure 3, [free tubulin] and [polymerized tubulin] from each run were averaged over a period of time after polymer-mass steady state was reached. The time to reach this steady state depends on the number of stable MT seeds (see Supplemental Figure S2). For the simplified model, the averages of [free tubulin] and [polymerized tubulin] were taken from 120 to 150 min for five MT seeds and from 15 to 30 min for 100 and 500 MT seeds. For the detailed model, the averages were taken from 100 to 150 min for five MT seeds and from 30 to 60 min for 40 and 100 MT seeds. We were able to use a larger number of seeds in the simplified model than in the detailed model because it is more computationally efficient.