SPR analysis demonstrates that αIIbβ3 has similar affinity for fibrinogen and fibrin. Purified human αIIbβ3 binding to (A) immobilized fibrinogen and (B) soluble fibrin. Where indicated, purified integrin was treated with 15 µg/mL PT25-2 at room temperature for 20 minutes. Kinetic values were obtained by fitting data to a heterogenous ligand interaction model.