title: Activation of factor VIII and mechanisms of cofactor action.
abstract: The factor VIII procofactor circulates as a metal ion-dependent heterodimer of a heavy chain and light chain. Activation of factor VIII results from limited proteolysis catalyzed by thrombin or factor Xa, which binds the factor VIII substrate over extended interactive surfaces. The proteases efficiently cleave factor VIII at three sites, two within the heavy and one within the light chain resulting in alteration of its covalent structure and conformation and yielding the active cofactor, factor VIIIa. The role of factor VIIIa is to markedly increase the catalytic efficiency of factor IXa in the activation of factor X. This effect is manifested in a dramatic increase in the catalytic rate constant, k(cat), by mechanisms that remain poorly understood.
authors.affiliation: Departments of Biochemistry and Biophysics and Medicine, PO Box 712, University of Rochester School of Medicine, Rochester, 601 Elmwood Avenue, Rochester, NY 14642, USA. philip_fay@urmc.rochester.edu
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Fay
mesh_terms: D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D015536:Down-Regulation; D005169:Factor VIII / Q000737:chemistry / Q000378:metabolism; D015944:Factor VIIIa / Q000737:chemistry / Q000378:metabolism*; D015951:Factor Xa / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D009363:Neoplasm Proteins / Q000737:chemistry / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D009363:Neoplasm Proteins; D014841:von Willebrand Factor; D015944:Factor VIIIa; D005169:Factor VIII; D013917:Thrombin; D015951:Factor Xa; D003546:Cysteine Endopeptidases; C030910:cancer procoagulant