Effects of bending and unbending of α_Lβ₂ on its dissociation from ligand. (A–E) Force-dependent reciprocal off rates (A–C) or associated fractions (D and E) of the short-, intermediate (inter.)-, and long-lived states evaluated from simultaneously fitting the three-state model to the survival frequency and rupture probability versus lifetime data (Fig. S4) without switching (A) or postswitching (B) measured in Mn²⁺. All of these reciprocal off rates are superimposed in C. Each set of off rate versus force data in A–C is fitted by the Bell model (dashed lines), and the parameters are summarized in Table S1. Fractions in D and E refer to the percentages of short-, intermediate-, and long-lived states. (F and G) Comparison of calculated mean lifetimes of soft (k_mol < 0.5 pN/nm; F) and stiff (k_mol > 0.5 pN/nm; G) α_Lβ₂–ICAM-1 bonds with the respective postunbending (F) and postbending (G) mean lifetime calculations. (H) Comparison of reduced χ²s of the three-state and two-state model fits to all data. P-value from the F test is shown. Error bars represent SEM.