Radiolabeled DT binding inhibition by the recombinant truncated HBΔ-EGF and mature HB-EGF proteins. The specific bound 125I-DT is plotted against the concentration of competitors, the recombinant mature Mk HB-EGF (□, ▪) or the recombinant truncated HBΔ-EGF (▵, ▴), in the absence (□, ▵) or the presence (▪, ▴) of heparin (10 U/ml). The average from duplicate wells was calculated and plotted. Results are representative of at least two separate experiments.