Blocking plasminogen (Plg) binding to isolated plasminogen receptors (Plg-Rs) by Fab fragments. H2B-coated (A), α-enolase–coated (B), annexin 2–coated (trypsin-cleaved 15 μg annexin 2 was cleaved in 50 μL of 1 mg/mL trypsin immobilized onto sepharose beads suspended in 10 mM CaCl₂, 50 mM Tris-Cl [pH 7.4] for 2.5 h at 37°C) (C), or p11-coated (D) plates were preincubated with Fab (0–16 μM) fragments of antipeptide antibodies raised to the Plg binding sites in each candidate Plg-R. Nonimmune rabbit Fab (0–16 μM) was used as a control with each Plg-R. Alexa 488 Glu-Plg (1 μM) was added to coated plates, with or without 100 mM EACA, and incubated for 2 hours at 37°C. The wells were washed, and bound Plg was quantified in a fluorescence plate reader using an excitation wavelength of 485 nm and emission wavelength of 530 nm. Values in the presence of EACA, which was 5% to 8% of total binding, were subtracted to obtain the specific binding values displayed. Means of duplicate determinations are plotted. Each Fab inhibited Plg binding by 80% to 90% at 16 μM. Error bar indicates SD.