title: Modulation of the enzymatic activity of alpha-thrombin by polyanions: consequences on intrinsic activation of factor V and factor VIII.
abstract: The polyanions heparin and dermatan sulfate catalyze alpha-thrombin inhibition and can delay the onset of factor VIII and factor V necessary for intrinsic prothrombin activation to begin in plasma. These polyanions bind alpha-thrombin at its anion-binding exosite(s), structural domain(s) occupancy of which may alter the properties of the fibrin(ogen) recognition exosite of alpha-thrombin. We compared how such four polyanions influenced factor VIII and factor V activation during intrinsic coagulation. A pentasaccharide with high affinity for antithrombin III and the C-terminal dodecapeptide fragment of hirudin (hirugen) which occupy the anion-binding and fibrin(ogen) recognition exosites of alpha-thrombin, respectively, could not significantly inhibit factor VIII and factor V activation. In contrast, heparin and a bis-lactobionic acid, both of which catalyzed alpha-thrombin inhibition, could effectively inhibit factor VIII and factor V activation. These results suggest that occupancy of fibrin(ogen) or anion-binding exosites by itself does not provide a necessary and sufficient condition for catalysis of thrombin inhibition or the inhibition thrombin-mediated amplification reactions.
authors.affiliation: Canadian Red Cross Blood Transfusion Service, McMaster University, Hamilton, Ont.
authors.forename: F A
authors.initials: FA
authors.lastname: Ofosu
mesh_terms: D000595:Amino Acid Sequence; D000838:Anions / Q000494:pharmacology; D001665:Binding Sites; D003871:Dermatan Sulfate / Q000494:pharmacology*; D004187:Disaccharides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005165:Factor V / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005169:Factor VIII / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology*; D006629:Hirudins / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D009844:Oligosaccharides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D013917:Thrombin / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D000838:Anions; D004187:Disaccharides; D006629:Hirudins; D009842:Oligopeptides; D009844:Oligosaccharides; D010446:Peptide Fragments; C062510:hirugen; D003871:Dermatan Sulfate; C005608:lactobionic acid; C020924:phenylalanyl-prolyl-arginine methyl chloride; C049714:IC 831423; D005165:Factor V; D005169:Factor VIII; D005340:Fibrinogen; D006493:Heparin; D013917:Thrombin