title: Demonstration and characterization of specific binding sites for factor VIII/von Willebrand factor on human platelets.
abstract: The presence of specific Factor VIII/von Willebrand factor (FVIII/vWF) binding sites on human platelets has been demonstrated by using 125I-FVIII/vWF and washed human platelets. Binding is ristocetin-dependent and increases in proportion to the concentration of ristocetin from 0.2 to 1 mg/ml. Binding of 125I-FVIII/vWF to platelets can be competitively inhibited by unlabeled human or bovine FVIII/vWF, but not by human thrombin, fibrinogen, alpha 2-macroglobulin, equine collagen, or a lectin of Ricinus communis. Scatchard analysis of binding data indicated that the dissociation constant of FVIII/vWF receptors is 0.45--0.5 nM. There are 31,000 binding sites per platelet at 1 mg/ml of ristocetin concentration. The optimal pH range for binding is from 7.0 to 7.5. At a concentration of 2 mM, EGTA inhibits 86% of the binding; however, 20 mM of Ca++, Mg++, or EDTA have little effect. Binding sites for FVIII/vWF were found only on platelets, and no significant binding was detected with human erythrocytes or polymorphonuclear leukocytes.
mesh_terms: D001665:Binding Sites; D001779:Blood Coagulation Factors / Q000502:physiology*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D005169:Factor VIII / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D011485:Protein Binding; D012310:Ristocetin / Q000494:pharmacology; D014841:von Willebrand Factor / Q000502:physiology*
chemical_list: D001779:Blood Coagulation Factors; D014841:von Willebrand Factor; D012310:Ristocetin; D004533:Egtazic Acid; D005169:Factor VIII; D004492:Edetic Acid; D008274:Magnesium; D002118:Calcium