FIGURE 4.

Force-dependent lifetimes of 1238-A1 bonds with different GPIbα preparations. Plots of lifetime versus force of 1238-A1 bonds with GPIbα from lysates of platelets (A, black squares) or CHOαβ9 cells (B, black diamonds) captured on targets or with glycocalicin (C, black circles) coated on targets. The curve of 1238-A1 bonds with GPIbα expressed on platelets (red squares) were used as the standard to compare the properties of purified proteins. The previous data of 1238-A1 interaction with platelet lysate GPIbα from Fig. 2A were replotted for comparison in A. Lifetimes (mean ± S.E. of >20 measurements per point) were measured by the thermal fluctuation assay (closed symbols) at zero force and by the force clamp assay at nonzero forces (open symbols).