title: Membrane binding events in the initiation and propagation phases of tissue factor-initiated zymogen activation under flow.
abstract: This study investigates the dynamics of zymogen activation when both extrinsic tenase and prothrombinase are assembled on an appropriate membrane. Although the activation of prothrombin by surface-localized prothrombinase is clearly mediated by flow-induced dilutional effects, we find that when factor X is activated in isolation by surface-localized extrinsic tenase, it exhibits characteristics of diffusion-mediated activation in which diffusion of substrate to the catalytically active region is rate-limiting. When prothrombin and factor X are activated coincident with each other, competition for available membrane binding sites masks the diffusion-limiting effects of factor X activation. To verify the role of membrane binding in the activation of factor X by extrinsic tenase under flow conditions, we demonstrate that bovine lactadherin competes for both factor X and Xa binding sites, limiting factor X activation and forcing the release of bound factor Xa from the membrane at a venous shear rate (100 s(-1)). Finally, we present steady-state models of prothrombin and factor X activation under flow showing that zymogen and enzyme membrane binding events further regulate the coagulation process in an open system representative of the vasculature geometry.
authors.affiliation: Department of Biochemistry, University of Vermont College of Medicine, Colchester, Vermont 05446, USA.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Haynes
authors.forename: Yves C
authors.initials: YC
authors.lastname: Dubief
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: Mann
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004058:Diffusion; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D005170:Factor X / Q000378:metabolism; D015951:Factor Xa / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D009363:Neoplasm Proteins / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D011485:Protein Binding; D011516:Prothrombin / Q000378:metabolism; D013925:Thromboplastin / Q000378:metabolism*
chemical_list: D004792:Enzyme Precursors; D009363:Neoplasm Proteins; D010743:Phospholipids; D011516:Prothrombin; D005170:Factor X; C025337:Factor IIa; D013925:Thromboplastin; D015951:Factor Xa; D003546:Cysteine Endopeptidases; C030910:cancer procoagulant