Binding of Hx-heme to immobilized LRP/CD91. (A) Inhibition of binding of ¹²⁵I-labeled Hx-heme by unlabeled Hx-heme complexes and noncomplexed Hx. (B) Effect on binding of ¹²⁵I-labeled Hx-heme by RAP (100 μg/mL), EDTA (10 mM), rabbit anti-LRP/CD91 IgG (300 μg/mL), nonimmune rabbit IgG (300 μg/mL), and activated α₂-macroglobulin (α₂M^*, 100 μg/mL). All values in panels A and B, representing the measured radioactivity in percentage of the added radioactivity, are the mean ± 1 SD of triplicate determinations. Each 200-μL well was incubated with 3000 cpm ¹²⁵I-Hx-heme (∼0.5 ng). (C) Surface plasmon resonance analysis of the binding of Hx (500 nM and 5 μM) and heme (500 nM) to immobilized LRP/CD91. (D) Surface plasmon resonance analysis of the binding of Hx-heme (50 nM to 5 μM) to immobilized LRP/CD91.