title: Modulation of human prothrombin activation on phospholipid vesicles and platelets using monoclonal antibodies to prothrombin fragment 2.
abstract: Prothrombin contains two kringle domains that are removed during activation to the blood clotting enzyme alpha-thrombin. By analogy with other kringle-containing proteins the prothrombin kringles may play a role in the protein-protein interactions necessary for prothrombin activation. Four monoclonal antibodies to prothrombin kringle 2 have been produced against human prothrombin, and a fifth monoclonal antibody was produced against a synthetic peptide consisting of amino acid residues 216-231 of kringle 2. Each antibody was tested for its ability to block prothrombin activation by factor Xa. In the presence of phosphatidylcholine/phosphatidylserine vesicles and factor Va, two of the antibodies, alpha HII-3 and alpha HII-4, inhibited prothrombin activation at a 90 and 50% level, respectively. Two other monoclonal antibodies (alpha HII-6 and alpha HII-7) and the antipeptide antibody (alpha HII-5) had no effect on prothrombin activation. When factor Xa was the catalyst alone, antibody alpha HII-3 lost the ability to inhibit prothrombin activation whereas antibody alpha HII-4 again partially inhibited the reaction. When human platelets were the reaction surface, the patterns of inhibition by the anti-fragment 2 antibodies were identical to that observed with phospholipid vesicles. These data suggest a role for prothrombin fragment 2 in activation, possibly by mediating the interaction of substrate prothrombin with factor Xa or factor Va on the phospholipid surface.
authors.affiliation: Department of Biochemistry, University of Vermont College of Medicine, Burlington 05405.
authors.forename: W R
authors.initials: WR
authors.lastname: Church
authors.forename: L A
authors.initials: LA
authors.lastname: Ouellette
authors.forename: T L
authors.initials: TL
authors.lastname: Messier
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D001792:Blood Platelets / Q000378:metabolism*; D004789:Enzyme Activation; D015943:Factor Va / Q000378:metabolism; D015951:Factor Xa / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D011516:Prothrombin / Q000276:immunology / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D010743:Phospholipids; D015943:Factor Va; D011516:Prothrombin; D015951:Factor Xa