The recombinant (Bβ1–66)2 fragment was produced in E. coli and purified as previously described9 (link). This fragment was treated with thrombin to produce fibrin-related (β15–66)2 fragment using the previously described procedure21 (link). Human recombinant receptor-associated protein (RAP) was expressed in E. coli and purified as previously described22 (link). Mouse anti-hVLDLR monoclonal antibodies 1H5, 5F3, and 1H1023 (link) were kindly provided by Dr. D. Strickland (University of Maryland Baltimore). Anti-His(C-term) antibody (anti-His tag mAb) conjugated with HRP was from Invitrogen (Carlsbad, CA). Goat secondary anti-mouse polyclonal antibodies conjugated with HRP and HRP substrate SureBlue TMB were from KPL (Gaithersburg, MD). Cyanogen bromide-activated Sepharose 4B and Thrombin CleanCleave kit were obtained from Sigma (St. Louis, MO).