Figure 3.

Velocity dependence of the unbinding forces. (A) The maximum of the unbinding force distribution for the a⋅d duplex (10 bp) is shifted from 21 to 41 pN (from Gaussian fits) when increasing the retract velocity from 8 to 1,600 nm/s. The broadening of the distribution is partially attributable to an increase of noise in the force displacement curves at higher retract velocities (because the rate of data acquisition is constant, fewer deflection values are acquired to determine the force at higher velocities). (B) The dependence of the most probable unbinding force on the retract velocity for an a-tip against a b-surface (30 bp), c-surface (20 bp), and d-surface (10 bp) and linear fits to the respective data sets. The extrapolation to zero unbinding force gives an estimate for the thermal off-rate.