Fig. 6. Opposing kinetic and physical effects give rise to robustness in trigger wave speeds.

a Comparing the effect sizes of changes in rate constant, effective diffusion coefficient, and concentration. Effect size is defined as fold change relative to 1 x cytoplasmic concentration. For simplicity, the data for cytoplasmic concentrations < 0.3x, where the concentration effect dominates, are omitted. b, e Effective diffusion coefficients of AF488-BSA in XB buffers of various sucrose concentrations (b; no BSA present) or BSA concentrations (e; no sucrose present) as determined by FCS. Means ± 90% CI (n = 1) calculated from 3 measurements are shown. AF488-BSA diffusion in 1 x extract can be mimicked by ~0.8 M sucrose or ~150 mg mL⁻¹ BSA. c, f Apoptotic trigger wave speeds with extracts diluted with buffer (black data points) or a viscogen (red data points) and compared with theoretical curves (dashed lines). Crowding effects are quantified by the parameter $g$. For apoptotic trigger waves, $g$ is ~1.3 (Fig. 5b) and is 0 if crowding effects are absent. We note that, in the case of $g=0$, wave speed $v$ is proportional to the square root of total caspase 3/7 concentration $\sqrt{C_{rel}}$. Means ± S.E.M. (n = 3) are shown for sucrose-containing buffers (c). Means (n = 2) are shown for BSA-containing buffers (f). The curves were set to equal the measured wave speeds at 1 x cytoplasmic concentration for both sucrose-containing and BSA-containing buffers. Apoptotic wave speeds at 0.5 x cytoplasmic concentration are also plotted. We note the scaling can be approximated by a horizontal line for $g=1.3$ between 0.5 x and 1 x cytoplasmic extract, whereas for $g=0$, a straight line with a positive slope. d, g Apoptotic trigger wave speeds are plotted for a range of sucrose-containing (d) or BSA-containing buffers (g) at different cytoplasmic concentrations. Means ± S.E.M. (n = 3) are shown for sucrose-containing buffers (d) whereas means (n = 2) are shown for BSA-containing buffers (g). Straight lines were fitted to each sucrose (d) or BSA (g) concentration. Only buffer without sucrose or BSA manifest straight lines with slightly negative slopes. Viscogen-containing buffers, be it sucrose or BSA, manifest positive slopes. Source data are provided as a Source Data file.