Subject(s)
Factor X/chemistry , HIV Envelope Protein gp120/chemistry , HIV-1/chemistry , HLA-DQ Antigens/chemistry , HLA-DR Antigens/chemistry , Molecular Mimicry , Amino Acid Sequence , Epitopes/chemistry , Humans , Molecular Sequence Data , Protein Structure, Tertiary , Sequence Alignment , Sequence Homology, Amino AcidABSTRACT
Steady state kinetic studies have provided evidence for intrinsic prothrombinase activity of human factor X zymogen in a chromogenic assay system. Using a prothrombin substrate, kinetic parameters have been obtained for the action of factors X and Xa. The Km for prothrombin is of a different order of magnitude for the zymogen as compared with the active enzyme. Using a kinetic approach, we have obtained evidence for the binding of factor Xa zymogen to cofactors essential for the coagulant activity of factor Xa. Zymogen enzymatic activity is not inhibited by a specific serine proteinase inhibitor, (p-amidino-phenyl)methanesulfonyl fluoride (p-APMSF), a potent inhibitor of factor Xa. The apparent slow rate of zymogen inhibition by antithrombin III (AT III) as compared with the active enzyme suggests a different kind of zymogen-antithrombin interaction. Blood clotting studies paralleled the kinetic data. Factor X zymogen evidences factor VIII inhibitor bypassing activity (FEIBA) in an in vitro direct clotting system employing factor VIII deficient inhibitor plasma as substrate in both activated or nonactivated partial thromboplastin assay. Most significantly, zymogen coagulant is refractory to inhibition by p-APMSF or AT III. We conclude that a system consisting of factor X zymogen-phospholipid-factor Va can physiologically initiate blood clotting in the presence of inhibitors and may have a major role in the bypass mechanism of therapeutic prothrombin complex concentrate (PCC).
Subject(s)
Enzyme Precursors , Factor IX/metabolism , Factor X/metabolism , Prothrombin/metabolism , Antithrombin III/pharmacology , Blood Coagulation , Blood Coagulation Factors/physiology , Factor IXa , Humans , In Vitro Techniques , Kinetics , Phenylmethylsulfonyl Fluoride/analogs & derivatives , Phenylmethylsulfonyl Fluoride/pharmacology , Phospholipids/bloodABSTRACT
A case is reported in which massive extracorporeal blood clotting necessitated the discontinuance of leukapheresis and loss of the product. An investigation of the cause of the massive clotting is reported along with suggested precautions to prevent similar occurrences in pheresis programs.
Subject(s)
Blood Coagulation , Plasmapheresis , Anticoagulants/pharmacology , Citrates/pharmacology , HumansABSTRACT
Blue Dextran 2000 coupled covalently to agarose has been used as an affinity column for the rapid separation of human blood clotting Factor X. Factor X has been isolated with approximately 2000-fold purification from human citrated plasma and shows single-component behavior by sodium dodecyl sulfate gel electrophoresis. Affinity columns prepared with Blue Dextran chromophore (Cibacron blue) derivatized to agarose or Sepharose gave negative results. These studies have shown that Blue Dextran agarose possesses unique biospecific and nonbiospecific properties, both of which are essential to achieve resolution of Factor X from other vitamin K-dependent blood clotting factors.
