Influence of Zn²⁺ on VN binding to uPAR. (A) Binding of ¹²⁵I-VN to U937 cells was performed in the absence or presence of 50 μmol/L Zn²⁺ or 20 nmol/L uPA alone or added together as indicated. Data (mean ± SEM, n = 3) are expressed as specific binding (as determined by subtracting binding in the presence of excess unlabeled VN). (B) Binding of¹²⁵I-VN to immobilized uPAR was performed in the absence or presence of 50 μmol/L Zn²⁺ or 20 nmol/L uPA, respectively. Either no additives (▩) or 20 μg/mL MoAb R3 against uPAR (▨), 500 μmol/L 1-10-phenanthroline (), or 100 nmol/L PAI-1 (▤) were included as competitors. Data (mean ± SEM, n = 3) are expressed as specific binding (represented as percent of control). Similar results were obtained in at least three separate experiments.