Table 1.

Distance to the transition state from isoI (Δxf) and from isoII (Δxb), measured from the force-dependent transition rates between isoI and isoII for four different junctions. Errors represent SD from five different molecules each. Also shown is Δxeq, the distance between isoI and isoII, determined from force-dependent changes in the equilibrium constant. For junction BR, Δxeq deviates significantly from (Δxbxf) showing that dBR is not a valid reaction coordinate connecting isoI and isoII. In contrast, Δxeq = Δxb + Δxf within error for junctions XR and HR, showing that dXR and dHR are reaction coordinates valid from isoI to isoII.

XRXR-longHRBR
Δxb (nm) 1.5 (±0.3) 2.6 (±0.6) 2.4 (±0.5) 1.1 (±0.2)
Δxf (nm) 2.9 (±0.6) 7.7 (±1.5) 1.3 (±0.3) 0.37 (±0.2)
Δxeq (nm) 4.4 (±0.8) 9.9 (±2.6) 3.1 (±0.8) 0.7 (±0.2)
Δxb + Δxf (nm) 4.4 (±0.8) 10.3 (±2.0) 3.6 (±0.5) 1.5 (±0.3)