Scatchard analysis of ¹²⁵I-labeled disintegrins binding to resting platelets (○) and to ADP-activated platelets (•). Platelets (2 × 10⁸/mL) were incubated with increasing concentration of ¹²⁵I-labeled echistatin (A), D27W echistatin (B), and echistatin 1-41 (C) for 15 minutes at room temperature and then 400 μL of platelet suspension was placed over silicone oil and centrifugated. The radioactivities of supernatant and pellet were measured with a γ-counter. Nonspecific binding was measured after preincubation of platelets (5 minutes at room temperature) with 5 mmol/L EDTA. The results are means from three independent experiments.