¹²⁵I-labeled ATF binding to VSMCs. The upper panel shows the competitive displacement curve for the specific binding of ¹²⁵I-labeled amino-terminal fragment of uPA to VSMCs, after subtraction of nonspecific binding (<15% of total binding). Data shown are the mean ± SD of duplicate determinations. The inset shows a Scatchard transformation of these data. In three independent experiments, the binding constants were determined as kd = 1.2 ± 0.4 nmol/L, B_max = 60,000 ± 16,000 sites/cell (mean ± SD). The lower panel shows chemical cross-linking of ¹²⁵I-labeled ATF to Triton X-114 lysates of VSMCs. Lane 1, recombinant soluble uPAR; lane 2, aqueous phase of X-114 lysate; lane 3, detergent phase of X-114 lysate; lane 4, ¹²⁵I-labeled ATF cross-linked alone. The ATF:uPAR complex in lane 3 migrates with an apparent molecular weight of 70 kD. The band of 35 kD present in all lanes represents cross-linked dimers of ATF.