Figure 7.

(a) Velocity of actin filament as a function of ATP at two different HMM densities; 100 μg/ml (circle) and 600 μg/ml (diamond). Solid line is Michaelis-Menten fit to filament velocity for a range of [MgATP]. V_max and K_m correspond to 5.5 ± 0.3 μm/s and 0.3 ± 0.03 mM respectively. (b) Double reciprocal plot of (a); value of d = 10 nm was used in the calculations. Data could be described using two linear fits for high and low ATP conditions. At high ATP (>0.5 mM) we calculated k_−ADP = 625 ± 139 s⁻¹ and k_+ATP = 1.6 ± 0.14 × 10⁶ M⁻¹ s⁻¹ using equation 4. At low ATP (<0.5 mM) we calculated k_−ADP = 356.6 ± 74.6 s⁻¹ and k_+ATP = 3.09 ± 0.24 × 10⁶ M⁻¹ s⁻¹. Inset shows the points and fit at high ATP for better visualization. Each point corresponds to an average from three different experiments with 30 filaments each. Error bars denote standard error.