title: High molecular weight kininogen binds to unstimulated platelets.
abstract: Studies were performed to determine if the unstimulated platelet membrane has a site for high molecular weight kininogen (HMWK) binding. 125I-HMWK bound to unstimulated platelets. Zn++ was required for 125I-HMWK binding to unstimulated platelets and binding was maximal at 50 microM Zn++. Neither Mg++ nor Ca++ substituted for Zn++ in supporting 125I-HMWK binding to unstimulated platelets, and neither ion potentiated binding in the presence of 50 microM zinc. 125I-HMWK competed with equal affinity with HMWK for binding, and excess HMWK inhibited 125I-HMWK-platelet binding. Only HMWK, not prekallikrein, Factor XII, Factor XI, Factor V, fibrinogen, or fibronectin inhibited 125I-HMWK-platelet binding. 125I-HMWK binding to unstimulated platelets was 89% reversible within 10 min with a 50-fold molar excess of HMWK. Unstimulated platelets contained a single set of saturable, high affinity binding sites for 125I-HMWK with an apparent dissociation constant of 0.99 nM +/- 0.35 and 3,313 molecules/platelet +/- 843. These studies indicate that the unstimulated external platelet membrane has a binding site for HMWK that could serve as a surface to modulate contact phase activation.
mesh_terms: D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007704:Kininogens / Q000097:blood*; D008274:Magnesium / Q000378:metabolism; D008970:Molecular Weight; D013379:Substrate Specificity; D013917:Thrombin / Q000494:pharmacology; D015032:Zinc / Q000378:metabolism
chemical_list: D007704:Kininogens; D013917:Thrombin; D008274:Magnesium; D015032:Zinc; D002118:Calcium