Binding of intact/nicked β₂-GPI to Glu-plasminogen. (A) Binding of intact or nicked β₂-GPI to immobilized Glu-plasminogen was evaluated by ELISA using mouse monoclonal anti-β₂-GPI antibody Cof-22. Closed circles indicate the dose-dependent binding of nicked β₂-GPI to Glu-plasminogen, whereas open circles indicate that intact β₂-GPI is unable to bind to Glu-plasminogen. (B-C) Kinetic plot showing molecular interaction between Glu-plasminogen and intact or nicked β₂-GPI. Intact β₂-GPI or nicked β₂-GPI binding to Glu-plasminogen was detected using IAsys, an optical biosensor as described in “Patients, materials, and methods.” Binding extent (arc sec) was compared between intact and nicked β₂-GPI (B). Obtained on-rate constant (k_on) for nicked β₂-GPI was plotted and fitted using linear regression to find the intercept and gradient (C). A formula for determining the association rate constant (k_ass) and dissociation rate constant (k_diss) is as follows: k_on = k_diss+ k_ass [ligand]. Error bars indicate SDs.