title: Ristocetin-dependent reconstitution of binding of von Willebrand factor to purified human platelet membrane glycoprotein Ib-IX complex.
abstract: Whether the human platelet membrane glycoprotein (GP) Ib-IX complex is the receptor for ristocetin-dependent binding of von Willebrand factor (vWF) has been examined by reconstitution with the purified components using a solid-phase bead assay. Purified GP Ib-IX complex was bound and orientated on the beads via a monoclonal antibody, FMC 25, directed against the membrane-associated region of the complex. Specific binding of 125I-labeled vWF to the GP Ib-IX complex coated beads was strictly ristocetin dependent with maximal binding occurring at ristocetin concentrations greater than or equal to 1 mg/mL. Ristocetin-dependent specific binding of 125I-labeled vWF was saturable. The observed binding was specific to the interaction between vWF and the GP Ib-IX complex since there was no ristocetin-dependent specific binding of vWF if the physicochemically related platelet membrane glycoprotein, GP IIb, was substituted for the GP Ib-IX complex in a corresponding bead assay. Further, neither bovine serum albumin nor other adhesive glycoproteins, such as fibrinogen or fibronectin, specifically bound to the GP Ib-IX complex in the presence of ristocetin. Ristocetin-dependent binding of vWF to platelets and to GP Ib-IX complex coated beads was inhibited by monoclonal antibodies against a 45,000 molecular weight N-terminal region of GP Ib but not by monoclonal antibodies directed against other regions of the GP Ib-IX complex. Similar correspondence between platelets and purified GP Ib-IX complex with respect to the ristocetin-dependent binding of vWF was obtained with anti-vWF monoclonal antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D002417:Cattle; D000939:Epitopes / Q000032:analysis; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D010980:Platelet Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*; D011485:Protein Binding; D012310:Ristocetin / Q000494:pharmacology*; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D000939:Epitopes; D007457:Iodine Radioisotopes; D010980:Platelet Membrane Glycoproteins; D014841:von Willebrand Factor; D012310:Ristocetin