title: Further characterization of wheat germ agglutinin interaction with human platelets: exposure of fibrinogen receptors.
abstract: It was previously shown that Wheat germ agglutinin, (WGA)-induced platelet activation occurred when only 17% of the lectin binding sites were occupied on the platelet surface and WGA caused the release of a platelet constituent which in turn participates in the observed effect. We now further define the platelet activation induced by WGA: the lectin induces a binding of fibrinogen to specific surface receptors. 125I-fibrinogen binding increases with the WGA concentration from 5 to 15 micrograms/ml. Binding occurs without addition of exogenous calcium; its analysis demonstrated 54,000 sites with a Ka = 0.8 X 10(6) M-1. Addition of 1 mM Ca2+ enhances the 125I-fibrinogen binding and reveals a second class of sites with higher affinity (9200 sites, Ka = 0.17 X 10(8) M-1). This 125I-fibrinogen binding is totally abolished by EDTA, ATP and arginine, and inhibited by 75% by CP/CPK; cyclooxygenase inhibitors and PGE1 also reduce the fibrinogen binding. Thus the WGA-induced fibrinogen binding is release-dependent and responsible for the aggregation process but not for the agglutinating effect of the lectin.
mesh_terms: D000527:Alprostadil / Q000494:pharmacology; D001120:Arginine / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000648:ultrastructure; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000494:pharmacology; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000187:drug effects* / Q000502:physiology; D011485:Protein Binding; D014909:Wheat Germ Agglutinins / Q000494:pharmacology*
chemical_list: D010980:Platelet Membrane Glycoproteins; D014909:Wheat Germ Agglutinins; D005340:Fibrinogen; D001120:Arginine; D004492:Edetic Acid; D000527:Alprostadil