Figure 5.

[P_i] dependence of actin sliding velocities and the rate of actin filament breaking. (A) Actin filament break times, τ_break, were measured in the presence of 30 mM P_i at 30 μM ATP for filaments < 3.3 μm and plotted in a histogram (n = 224). The data were fitted to a single exponential (solid line) to obtain the actin filament lifetime (τ_break). (B) Actin filament break times, τ_break, were measured in the presence 30 μM ATP with no added P_i for filaments < 3.3 μm and plotted in a histogram (n = 279). The data were fitted with a single exponential (solid line) to obtain the average time to break (τ_break). (C) Values for the actin filament lifetime (τ_break) obtained with (dark squares) and without (white squares) added P_i at 30 μM ATP are plotted both for actin filament lengths < 3.3 μm and for actin filament lengths between 3.3 and 6.6 μm. (D) For all actin filament lengths, mean actin sliding velocities (grey bars), normalized to 1.8 μm·sec⁻¹, and the rates of actin breaking (white bars), normalized to 0.029 sec⁻¹, obtained in the presence and absence of 30 mM P_i at 30 μM ATP are plotted, showing that the inhibition of V by P_i corresponds to a decrease in interhead forces.