Figure 3.

Calponin delayed the onset of strain stiffening in cross-linked actin networks. (A) The bulk rheology stress-strain curves from Fig. 2 with (black lines) or without (gray lines) a twofold molar excess of calponin, normalized by the yield stress, ${\sigma }_{max}$, and yield strain, ${\gamma }_{max}$, of each curve. (B) The differential elastic modulus, $K^{\text{'}}$, of the stress-strain curves shown in A, normalized by ${\gamma }_{max}$ and $K^{\text{'}}$ of each curve. Samples with and without calponin were similar, with the exception of a delayed onset of strain stiffening in samples with calponin. (C) The onset of strain stiffening, ${\gamma }_{crit}$, was defined as the strain at which the linear elastic modulus and the power-law fit to the stress-strain curve in the nonlinear stiffening regime intersected (dashed lines). Shown are two stress-strain curves for samples with (black) and without (gray) a twofold molar excess of basic calponin. (D) Onset of strain stiffening was increased from 10.0 ± 0.6% without calponin to 14.9 ± 1.0% with calponin (p < 0.01). Error bars represent the mean ± SE.