DF interacts with heparin-binding proteins in a concentration-dependent manner. Either PDGF BB (50 nmol/L, A), VEGF (150 nmol/L, B), or collagen I (30 nmol/L, C) was incubated in 0.1 mol/L Tris-HCL, pH 7.4, with ClRNH³²P-OdT₁₈ at the stated concentrations for 1 hour at 37°C. The sample buffer was then added, and the mixture was boiled and subjected to 12% PAGE. Unreacted oligomer ran off the bottom of the gel and is not shown. The gel bands in left insert were quantitated by laser densitometry. Shown is a plot of relative band intensity versus probe oligodeoxynucleotide concentration. Right insert: Double-reciprocal plot of these data. The value of apparent K_d (−1/x intercept) for PDGF BB, VEGF, and collagen I were 5, 34, and 0.6 μmol/L, respectively.