Binding of α₂β₁ and I domain to GFOGER: effect of thiol blocking and of inhibition of disulfide exchange and PDI. (A) Adhesion to GFOGER-GPP of purified α₂β₁ or recombinant I domain was measured using a monoclonal antibody to α₂ integrin I domain as described in “Methods.” Data are mean absorbance (± SD) of 4 experiments, each performed in triplicate. (B) The α₂β₁ from human platelets was biotinylated then incubated with increasing concentrations of DTNB, 30 mM bacitracin (Bac), or RL-90, as in Figure 4, and allowed to adhere to immobilized GFOGER-GPP as described in “Methods.” Adhesion was measured using HRP-linked streptavidin and data shown are mean ± SD from 3 experiments, each performed in triplicate. Residual adhesion is expressed relative to untreated controls. (C) Recombinant α₂ I domain was incubated with 10 mM DTNB or 30 mM bacitracin (Bac), allowed to adhere to immobilized GFOGER-GPP, and estimated using anti-GST as described in “Methods.” Data are mean ± SD from 3 experiments each performed in triplicate concomitantly with panel A. Residual adhesion is expressed relative to untreated controls.