The Role of Factor VIII in the Activation of Human Blood Coagulation Factor X by Activated Factor IX

1985 ◽  
Vol 54 (03) ◽  
pp. 654-660 ◽  
Author(s):  
K Mertens ◽  
A van Wijngaarden ◽  
R M Bertina
Keyword(s):  
Factor Viii ◽  
Substrate Inhibition ◽  
Factor Xa ◽  
Coagulation Factor ◽  
Catalytic Efficiency ◽  
Enzyme Concentration ◽  
Factor Ix ◽  
Factor X ◽  
Factor Ixa

SummaryThe role of factor VIII in the activation of human factor X by factor IXa, Ca2+ and phospholipid has been investigated. Factor VIII stimulated the factor Xa formation after activation by factor Xa or thrombin; the activity of thrombin-activated factor VIII was about 4-fold that of factor Xa-activated factor VIII. The isolated procoagulant moiety of the factor VIII complex behaved identically to the complete complex, whereas the von Willebrand factor moiety did not participate in the factor Xa formation. Thrombin-activated factor VIII complex (factor Villa) was used to study the effect of factor Villa in kinetic experiments. The results revealed a complex kinetic behaviour, including substrate inhibition and non-linearity of the reaction rate with the enzyme concentration. Using previously obtained insight into the kinetics of factor X activation in the absence of factor VIII, the results were found to support the hypothesis that factor Villa participates in the factor Xa formation in a complex with phospholipid-bound factor IXa; the formation of the factor VUIa-factor IXa complex then increases the catalytic efficiency of the factor IXa by 500-fold.

scholarly journals The contribution of Ca2+ and phospholipids to the activation of human blood-coagulation Factor X by activated Factor IX

1984 ◽  
Vol 223 (3) ◽  
pp. 607-615 ◽  
Author(s):  
K Mertens ◽  
R M Bertina
Keyword(s):  
Human Factor ◽  
Factor Xa ◽  
Coagulation Factor ◽  
Factor Ix ◽  
Activate Factor ◽  
Factor X ◽  
Formation Kinetic ◽  
Factor Ixa ◽  
Fold Stimulation

The role of the cofactors Ca2+ and phospholipid in the activation of human Factor X by Factor IXa was investigated. By use of a sensitive spectrophotometric Factor Xa assay, it was demonstrated that human Factor IXa can activate Factor X in the absence of cofactors. The presence of Ca2+ as the only cofactor resulted in a 7-fold stimulation of the Factor Xa formation. Kinetic analysis of the Ca2+-stimulated reaction showed that the apparent Km of Factor X was 4.6 microM, whereas the apparent Vmax. for Factor Xa formation was 0.0088 mol of Xa/min per mol of IXa. The presence of phospholipid as the only cofactor had no effect on the rate of Factor Xa formation. However, a several-hundred-fold stimulation was observed when Ca2+ and phospholipid were present in combination. The activation of Factor X in the presence of Ca2+ and phospholipid was found to be kinetically heterogeneous, involving both phospholipid-bound and free reactants. Quantitative data concerning the phospholipid binding of Factors IXa and X were used to study the relation between the rate of Factor Xa formation and the binding of enzyme and substrate to the phospholipid membrane. The results support the hypothesis that phospholipid-bound Factor X is the substrate in the phospholipid-stimulated reaction; however, phospholipid-bound and free Factor IXa seem to be equally efficient in catalysing the activation of phospholipid-bound Factor X.

Activation of Human Coagulation Factor VIII by Activated Factor X, the Common Product of the Intrinsic and the Extrinsic Pathway of Blood Coagulation

1982 ◽  
Vol 47 (02) ◽  
pp. 096-100 ◽  
Author(s):  
K Mertens ◽  
R M Bertina
Keyword(s):  
Factor Viii ◽  
Human Factor ◽  
Intrinsic Factor ◽  
Factor Xa ◽  
Coagulation Factor ◽  
Factor X ◽  
Extrinsic Factor ◽  
Extrinsic Pathway ◽  
Factor Ixa ◽  
The Common

SummaryThe intrinsic activation of human factor X has been studied in a system consisting of purified factors and in plasma. In both these systems factor Xa stimulated the activation of factor X by factor IXa plus factor VIII This is due to the activation of factor VIII by factor Xa. When this factor Xa is formed via the extrinsic pathway, the extrinsic factor X activator functions as a stimulator of the intrinsic factor X activator.

scholarly journals Role of gamma-carboxyglutamic acid residues in the binding of factor IXa to platelets and in factor-X activation

Blood ◽  
1992 ◽  
Vol 79 (2) ◽  
pp. 398-405 ◽  
Author(s):  
R Rawala-Sheikh ◽  
SS Ahmad ◽  
DM Monroe ◽  
HR Roberts ◽  
PN Walsh
Keyword(s):  
Binding Sites ◽  
Factor Xa ◽  
Catalytic Efficiency ◽  
Factor Ix ◽  
Factor X ◽  
Apparent Dissociation Constant ◽  
Factor Ixa ◽  
Factor Viiia ◽  
Carboxyglutamic Acid ◽  
Factor X Activation

To study the requirements for factor-IXa binding to platelets and factor-X activation, we examined the consequences of chemical modification (factor IXMOD) or enzymatic removal (factor IXDES) of gamma-carboxyglutamic acid (Gla) residues. In the presence of factor VIIIa and factor X, there were 344 (+/- 52) binding sites/platelet for factor IXaMOD (apparent dissociation constant [kdapp] = 4.5 +/- 0.9 nmol/L) and 275 (+/- 35) sites/platelet for factor IXaDES (kdapp = 5.0 +/- 0.8 nmol/L) compared with 580 (+/-65) sites/platelet for normal factor IXa (factor IXaN) (kdapp = 0.61 +/- 0.1 nmol/L) and 300 (+/-62) sites/platelet for factor IX (kdapp = 2.9 +/- 0.29 nmol/L). The concentrations of factor IXaN, factor IXaMOD and factor IXaDES required for half-maximal rates of factor-Xa formation were 0.67 nmol/L, 3.5 nmol/L, and 6.7 nmol/L. Whereas maximal velocities (Vmax) of factor Xa formation by factor IXaMOD (approximately 0.8 nmol/L.min-1) and factor IXaN (approximately 10.5 nmol/L.min-1), turnover numbers (kcat expressed as moles of factor Xa formed per minute per mole of factor IXa bound), and values of catalytic efficiency (kcat/Km) were normal, indicating that the decreased rates of factor X activation observed with factor IXaMOD and factor IXaDES are solely a consequence of the abnormal binding of these proteins to thrombin-activated platelets in the presence of factor VIIIa and factor X. Thus, factor IXa binding to platelets is mediated in part, but not exclusively, by high-affinity Ca2+ binding sites in the Gla domain of factor IX.

scholarly journals Role of gamma-carboxyglutamic acid residues in the binding of factor IXa to platelets and in factor-X activation

Blood ◽  
1992 ◽  
Vol 79 (2) ◽  
pp. 398-405 ◽  
Author(s):  
R Rawala-Sheikh ◽  
SS Ahmad ◽  
DM Monroe ◽  
HR Roberts ◽  
PN Walsh
Keyword(s):  
Binding Sites ◽  
Factor Xa ◽  
Catalytic Efficiency ◽  
Factor Ix ◽  
Factor X ◽  
Apparent Dissociation Constant ◽  
Factor Ixa ◽  
Factor Viiia ◽  
Carboxyglutamic Acid ◽  
Factor X Activation

Abstract To study the requirements for factor-IXa binding to platelets and factor-X activation, we examined the consequences of chemical modification (factor IXMOD) or enzymatic removal (factor IXDES) of gamma-carboxyglutamic acid (Gla) residues. In the presence of factor VIIIa and factor X, there were 344 (+/- 52) binding sites/platelet for factor IXaMOD (apparent dissociation constant [kdapp] = 4.5 +/- 0.9 nmol/L) and 275 (+/- 35) sites/platelet for factor IXaDES (kdapp = 5.0 +/- 0.8 nmol/L) compared with 580 (+/-65) sites/platelet for normal factor IXa (factor IXaN) (kdapp = 0.61 +/- 0.1 nmol/L) and 300 (+/-62) sites/platelet for factor IX (kdapp = 2.9 +/- 0.29 nmol/L). The concentrations of factor IXaN, factor IXaMOD and factor IXaDES required for half-maximal rates of factor-Xa formation were 0.67 nmol/L, 3.5 nmol/L, and 6.7 nmol/L. Whereas maximal velocities (Vmax) of factor Xa formation by factor IXaMOD (approximately 0.8 nmol/L.min-1) and factor IXaN (approximately 10.5 nmol/L.min-1), turnover numbers (kcat expressed as moles of factor Xa formed per minute per mole of factor IXa bound), and values of catalytic efficiency (kcat/Km) were normal, indicating that the decreased rates of factor X activation observed with factor IXaMOD and factor IXaDES are solely a consequence of the abnormal binding of these proteins to thrombin-activated platelets in the presence of factor VIIIa and factor X. Thus, factor IXa binding to platelets is mediated in part, but not exclusively, by high-affinity Ca2+ binding sites in the Gla domain of factor IX.

scholarly journals Functional assembly of intrinsic coagulation proteases on monocytes and platelets. Comparison between cofactor activities induced by thrombin and factor Xa.

1992 ◽  
Vol 176 (1) ◽  
pp. 27-35 ◽  
Author(s):  
M P McGee ◽  
L C Li ◽  
M Hensler
Keyword(s):  
Factor Viii ◽  
Factor Xa ◽  
Coagulation Factor ◽  
Coagulation Cascade ◽  
Factor X ◽  
Regulatory Pathways ◽  
Factor Ixa ◽  
Factor Viiia ◽  
Human Factor Viii

Generation of coagulation factor Xa by the intrinsic pathway protease complex is essential for normal activation of the coagulation cascade in vivo. Monocytes and platelets provide membrane sites for assembly of components of this protease complex, factors IXa and VIII. Under biologically relevant conditions, expression of functional activity by this complex is associated with activation of factor VIII to VIIIa. In the present studies, autocatalytic regulatory pathways operating on monocyte and platelet membranes were investigated by comparing the cofactor function of thrombin-activated factor VIII to that of factor Xa-activated factor VIII. Reciprocal functional titrations with purified human factor VIII and factor IXa were performed at fixed concentrations of human monocytes, CaCl2, factor X, and either factor IXa or factor VIII. Factor VIII was preactivated with either thrombin or factor Xa, and reactions were initiated by addition of factor X. Rates of factor X activation were measured using chromogenic substrate specific for factor Xa. The K1/2 values, i.e., concentration of factor VIIIa at which rates were half maximal, were 0.96 nM with thrombin-activated factor VIII and 1.1 nM with factor Xa-activated factor VIII. These values are close to factor VIII concentration in plasma. The Vsat, i.e., rates at saturating concentrations of factor VIII, were 33.3 and 13.6 nM factor Xa/min, respectively. The K1/2 and Vsat values obtained in titrations with factor IXa were not significantly different from those obtained with factor VIII. In titrations with factor X, the values of Michaelis-Menten coefficients (Km) were 31.7 nM with thrombin-activated factor VIII, and 14.2 nM with factor Xa-activated factor VIII. Maximal rates were 23.4 and 4.9 nM factor Xa/min, respectively. The apparent catalytic efficiency was similar with either form of factor VIIIa. Kinetic profiles obtained with platelets as a source of membrane were comparable to those obtained with monocytes. These kinetic profiles are consistent with a 1:1 stoichiometry for the functional interaction between cofactor and enzyme on the surface of monocytes and platelets. Taken together, these results indicate that autocatalytic pathways connecting the extrinsic, intrinsic, and common coagulation pathways can operate efficiently on the monocyte membrane.

scholarly journals The Role of Factor IXa and Factor VIII in the Activation of Factor X.

1977 ◽  
Author(s):  
Earl W. Davie ◽  
Gordon Vehar ◽  
Kazuo Fujikawa ◽  
Richard Di Scipio
Keyword(s):  
Factor Viii ◽  
Heavy Chain ◽  
Serine Proteases ◽  
Factor Xa ◽  
Basic Mechanism ◽  
Factor X ◽  
Amino Terminal ◽  
Factor Ixa ◽  
A Charge

Factor IXa and factor VIII participate in the middle phase of blood coagulation. These two proteins convert factor X to factor Xa in the presence of calcium ions and phospholipid. The coagulant activity of factor VIII is increased 50-100 fold by the addition of thrombin, and this activity is stabilized in the presence of CaCl2. The activated product (tentatively identified as activated factor VIII) was readily inhibited by diisopropyl phosphorofluoridate or antithrombin III, suggesting that it is a serine enzyme. The exact role of this enzyme in the conversion of factor X to factor Xa, however, is not known. When factor X (bovine or human) is converted to factor Xa, an activation peptide is cleaved from the amino-terminal end of the heavy chain. This gives rise to a new amino-terminal sequence of Ile-Val-Gly-Gly-in the heavy chain. No change occurs in the light chain during the activation reaction. These data indicate that the basic mechanism involved in the conversion of human and bovine factor X to factor Xa appears to be essentially identical and probably involves the formation of a charge relay system characteristic of the pancreatic serine proteases.

scholarly journals Activation of factor X by factors IXa and VIII; a specific assay for factor IXa in the presence of thrombin-activated factor VIII

Blood ◽  
1978 ◽  
Vol 52 (5) ◽  
pp. 928-940
Author(s):  
MB Hultin ◽  
Y Nemerson
Keyword(s):  
Factor Viii ◽  
Factor Ix ◽  
Constant Level ◽  
Specific Factor ◽  
Factor X ◽  
Intrinsic Pathway ◽  
Factor Ixa ◽  
Factor X Activation ◽  
Benzamidine Hydrochloride

We studied the activation of factor X by the intrinsic pathway of blood coagulation using a new assay of factor X activation. When factor X tritiated in its sialic acid residues is activated, activation can be measured by the release of tritiated activation peptide, and the initial rate of activation can be determined under varying conditions. In the presence of phospholipid and calcium ions, factor IXa activated factor X slowly without factor VIII, and this activation was blocked by a specific factor IX inhibitor. These data provide strong evidence that factor IXa is the enzyme responsible for factor X activation by the intrinsic pathway. The role of factor VIII was also investigated. Factor VIII could be reproducibly thrombin activated and then stabilized by the addition of 2 mM benzamidine hydrochloride; this suggests that inactivation is due to proteolysis. Neither unactivated nor thrombin-activated factor VIII produced factor X activation without factor IXa. With a constant level of factor IXa, factor X activation was directly proportional to the level of activated factor VIII. With a constant level of activated factor VIII, factor X activation was proportional to the factor IXa concentration. This observation was exploited to develop a specific, sensitive assay for factor IXa.

scholarly journals Activation of factor X by factors IXa and VIII; a specific assay for factor IXa in the presence of thrombin-activated factor VIII

Blood ◽  
1978 ◽  
Vol 52 (5) ◽  
pp. 928-940 ◽  
Author(s):  
MB Hultin ◽  
Y Nemerson
Keyword(s):  
Factor Viii ◽  
Factor Ix ◽  
Constant Level ◽  
Specific Factor ◽  
Factor X ◽  
Intrinsic Pathway ◽  
Factor Ixa ◽  
Factor X Activation ◽  
Benzamidine Hydrochloride

Abstract We studied the activation of factor X by the intrinsic pathway of blood coagulation using a new assay of factor X activation. When factor X tritiated in its sialic acid residues is activated, activation can be measured by the release of tritiated activation peptide, and the initial rate of activation can be determined under varying conditions. In the presence of phospholipid and calcium ions, factor IXa activated factor X slowly without factor VIII, and this activation was blocked by a specific factor IX inhibitor. These data provide strong evidence that factor IXa is the enzyme responsible for factor X activation by the intrinsic pathway. The role of factor VIII was also investigated. Factor VIII could be reproducibly thrombin activated and then stabilized by the addition of 2 mM benzamidine hydrochloride; this suggests that inactivation is due to proteolysis. Neither unactivated nor thrombin-activated factor VIII produced factor X activation without factor IXa. With a constant level of factor IXa, factor X activation was directly proportional to the level of activated factor VIII. With a constant level of activated factor VIII, factor X activation was proportional to the factor IXa concentration. This observation was exploited to develop a specific, sensitive assay for factor IXa.

scholarly journals In Hemophilia Α Plasma Treated with Emicizumab, Factor IX Activation By Factor VIIa Drives Thrombin Generation

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 17-17
Author(s):  
Dougald Monroe ◽  
Mirella Ezban ◽  
Maureane Hoffman
Keyword(s):  
Factor Viii ◽  
Tissue Factor ◽  
Plasma Levels ◽  
Thrombin Generation ◽  
Hemophilia A ◽  
Factor Viia ◽  
Factor Ix ◽  
Factor X ◽  
Dose Dependent

Background.Recently a novel bifunctional antibody (emicizumab) that binds both factor IXa (FIXa) and factor X (FX) has been used to treat hemophilia A. Emicizumab has proven remarkably effective as a prophylactic treatment for hemophilia A; however there are patients that still experience bleeding. An approach to safely and effectively treating this bleeding in hemophilia A patients with inhibitors is recombinant factor VIIa (rFVIIa). When given at therapeutic levels, rFVIIa can enhance tissue factor (TF) dependent activation of FX as well as activating FX independently of TF. At therapeutic levels rFVIIa can also activate FIX. The goal of this study was to assess the role of the FIXa activated by rFVIIa when emicizumab is added to hemophilia A plasma. Methods. Thrombin generation assays were done in plasma using 100 µM lipid and 420 µM Z-Gly-Gly-Arg-AMC with or without emicizumab at 55 µg/mL which is the clinical steady state level. The reactions were initiated with low (1 pM) tissue factor (TF). rFVIIa was added at concentrations of 25-100 nM with 25 nM corresponding to the plasma levels achieved by a single clinical dose of 90 µg/mL. To study to the role of factor IX in the absence of factor VIII, it was necessary to create a double deficient plasma (factors VIII and IX deficient). This was done by taking antigen negative hemophilia B plasma and adding a neutralizing antibody to factor VIII (Haematologic Technologies, Essex Junction, VT, USA). Now varying concentrations of factor IX could be reconstituted into the plasma to give hemophilia A plasma. Results. As expected, in the double deficient plasma with low TF there was essentially no thrombin generation. Also as expected from previous studies, addition of rFVIIa to double deficient plasma gave a dose dependent increase in thrombin generation through activation of FX. Interestingly addition of plasma levels of FIX to the rFVIIa did not increase thrombin generation. Starting from double deficient plasma, as expected emicizumab did not increase thrombin generation since no factor IX was present. Also, in double deficient plasma with rFVIIa, emicizumab did not increase thrombin generation. But in double deficient plasma with FIX and rFVIIa, emicizumab significantly increased thrombin generation. The levels of thrombin generation increased in a dose dependent fashion with higher concentrations of rFVIIa giving higher levels of thrombin generation. Conclusion. Since addition of FIX to the double deficient plasma with rFVIIa did not increase thrombin generation, it suggests that rFVIIa activation of FX is the only source of the FXa needed for thrombin generation. So in the absence of factor VIII (or emicizumab) FIX activation does not contribute to thrombin generation. However, in the presence of emicizumab, while rFVIIa can still activate FX, FIXa formed by rFVIIa can complex with emicizumab to provide an additional source of FX activation. Thus rFVIIa activation of FIX explains the synergistic effect in thrombin generation observed when combining rFVIIa with emicizumab. The generation of FIXa at a site of injury is consistent with the safety profile observed in clinical use. Disclosures Monroe: Novo Nordisk:Research Funding.Ezban:Novo Nordisk:Current Employment.Hoffman:Novo Nordisk:Research Funding.

scholarly journals The anticoagulant mechanism of action of heparin in contact-activated plasma: inhibition of factor X activation

Blood ◽  
1985 ◽  
Vol 65 (5) ◽  
pp. 1226-1231 ◽  
Author(s):  
TB McNeely ◽  
MJ Griffith
Keyword(s):  
Antithrombin Iii ◽  
Factor Xa ◽  
Coagulation Factors ◽  
Factor Ix ◽  
Factor X ◽  
Clotting Time ◽  
Intrinsic Pathway ◽  
Blood Coagulation Factors ◽  
Factor Ixa ◽  
Factor X Activation

Abstract The effects of heparin on the activation of blood coagulation factors IX and X in contact-activated plasma were determined in the present study. In the presence and absence of 0.5 U/mL heparin, the amounts of factor IX that were cleaved 30 minutes after the addition of calcium and phospholipid to plasma exposed to glass (ie, contact activated) were essentially identical. In the absence of heparin, however, the plasma clotting time was between three and four minutes, while in the presence of heparin, the clotting time was approximately 40 minutes. More factor IXa was inhibited by antithrombin III in the presence of heparin than in its absence, but factor IXa levels sufficient for factor X activation appeared to be present in the heparinized plasma. Neither an increase in factor Xa nor a decrease in factor X was detected, however, in heparinized plasma. We conclude that the step in the intrinsic pathway of coagulation that is inhibited in the presence of heparin is at the level of factor X activation.

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