scholarly journals Demonstration and characterization of specific binding sites for factor VIII/von Willebrand factor on human platelets.

1979 ◽  
Vol 63 (4) ◽  
pp. 656-664 ◽  
Author(s):  
K J Kao ◽  
S V Pizzo ◽  
P A McKee
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Binding Sites ◽  
Specific Binding ◽  
Human Platelets ◽  
Specific Binding Sites ◽  
Von Willebrand ◽  
Willebrand Factor

The Importance of the Carbohydrate Moiety of the Factor VIII/Von Willebrand Factor Protein in Binding to and Causing Agglutination of Human Platelets

1979 ◽  
Author(s):  
H.R. Gralnick ◽  
D.K. Morisato
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Binding Sites ◽  
Human Platelets ◽  
Galactose Oxidase ◽  
Scatchard Analysis ◽  
Human Fibrinogen ◽  
Number Of Binding Sites ◽  
Von Willebrand ◽  
Willebrand Factor

We have investigated the binding of radiolabelled factor VIII/von Willebrand factor (f. VIII/vWf) protein to human platelets (P) in the presence of ristocetin (R). In these atudies we have delineated the importance of the carbohydrate (CHO) moiety(s) in both the binding to the P and in cauaing agglutination of P. Binding of the f.VIII/vWf protein to human P was time and temperature dependent and dependent on the concentration of R. Binding was specific in that it could not be blocked by human fibrinogen but was inhibited by unlabelled f.VIII/vWf protein. In studies utilizing varying amounts of the f.VIII/vWf protein or by varying the number of P in the assay, the number of binding sites for the f. VIII/vWf protein were estimated at 9,500-9,800 per platelet. Scatchard analysis revealed 11,000 binding sites with 3,600 of high affinity and 7,400 of low affinity. Removal of the sialic acid of the f.VIII/vWf protein resulted in no significa nt change in its ability to bind to the P surface or cause agglutination in the presence, IR. Removal of the galactose by 6-galactosijase resulted in a 75% reduction of binding of the f.VIII/vWf protein and a 91% decrease in the agglutination of human P. Similar studies with galactose oxidase showed that oxidation of the penultimate galactose residue s results in a decrease in agglutination comparable to that seen with 6-galactosidase treatment. These studies indicate that the CHO moiety of the f.VIII/vWf protein is important in both binding to the P surface as well as causing agglutination of human P.

The Binding Of 125I-Von Willebrand Factor To Human Platelets In The Presence Of Ristocetin

1981 ◽  
Author(s):  
P Silber ◽  
T H Finlay
Keyword(s):  
Von Willebrand Factor ◽  
Binding Sites ◽  
Binding Constant ◽  
Specific Binding ◽  
Human Platelets ◽  
Scatchard Analysis ◽  
Binding Data ◽  
Number Of Binding Sites ◽  
Von Willebrand ◽  
Willebrand Factor

The effect of ristocetin on the binding of 125I-porcine von Willebrand factor to human platelets was studied. Previously, we had shown that 125I-porcine von Willebrand factor binds to human platelets in the absence of ristocetin. The present work demonstrates that binding is stimulated by ristocetin and this stimulation is maximal at a ristocetin concentration of 2 mg/ml. At a ristocetin concentration of 0.5 mg/ml, Scatchard analysis indicates a binding constant of 5.18 × 10-9M and the presence of 105,000 binding sites. This compares with our previous finding, in the absence of ristocetin, of a binding constant of 2.92 × 10-7M and 4760 binding sites. These binding data assume the porcine von Willebrand factor to be a tetramer with a molecular weight of 9 × 105. This study indicates that ristocetin causes tighter binding and increases the number of binding sites on human platelets for porcine von Willebrand factor. Unlabelled porcine von Willebrand factor competitively inhibits the specific binding of the labelled protein and gives a binding constant of 0.17 × 10-9M. Similar results were obtained using human von Willebrand factor.

scholarly journals Selective binding of the factor VIII/von Willebrand factor protein to human platelets

Blood ◽  
1980 ◽  
Vol 55 (1) ◽  
pp. 9-15 ◽  
Author(s):  
DK Morisato ◽  
HR Gralnick
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Binding Sites ◽  
Human Platelets ◽  
Galactose Oxidase ◽  
Scatchard Analysis ◽  
Potassium Borohydride ◽  
Human Factor Viii ◽  
Von Willebrand ◽  
Willebrand Factor

Abstract The factor VIII/von Willebrand factor protein was radiolabeled after modification by galactose oxidase and reduction with tritiated potassium borohydride. This mild efficient method for labeling resulted in retention of over 90% of the biologic activities of the factor VIII/von Willebrand factor protein. Binding of this protein to platelets was found to be specific, and binding sites could be saturated in the presence of ristocetin. However, binding was highly dependent on ristocetin concentration, as the number of human factor VIII/von Willebrand factor molecules bound per platelet was a function of the ristocetin concentration. At a ristocetin concentration of 0.55 mg/ml, each platelet binds approximately 11,000 factor VIII/von Willebrand factor molecules per platelet. Scatchard analysis of the concentration-dependent binding sites yielded a hyperbolic plot that appeared to be related to the existence of two classes of binding sites. The higher affinity class had a Kd of 3.7 x 10(-10) M 3500 sites/platelet, while the lower affinity class had a Kd of 2.35 x 10(- 9) M and a capacity of 7500 sites/platelet. As with ristocetin-induced platelet agglutination, the carbohydrate content plays a significant role in the binding of the factor VIII/von Willebrand factor protein to the platelet.

scholarly journals Selective binding of the factor VIII/von Willebrand factor protein to human platelets

Blood ◽  
1980 ◽  
Vol 55 (1) ◽  
pp. 9-15 ◽  
Author(s):  
DK Morisato ◽  
HR Gralnick
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Binding Sites ◽  
Human Platelets ◽  
Galactose Oxidase ◽  
Scatchard Analysis ◽  
Potassium Borohydride ◽  
Human Factor Viii ◽  
Von Willebrand ◽  
Willebrand Factor

The factor VIII/von Willebrand factor protein was radiolabeled after modification by galactose oxidase and reduction with tritiated potassium borohydride. This mild efficient method for labeling resulted in retention of over 90% of the biologic activities of the factor VIII/von Willebrand factor protein. Binding of this protein to platelets was found to be specific, and binding sites could be saturated in the presence of ristocetin. However, binding was highly dependent on ristocetin concentration, as the number of human factor VIII/von Willebrand factor molecules bound per platelet was a function of the ristocetin concentration. At a ristocetin concentration of 0.55 mg/ml, each platelet binds approximately 11,000 factor VIII/von Willebrand factor molecules per platelet. Scatchard analysis of the concentration-dependent binding sites yielded a hyperbolic plot that appeared to be related to the existence of two classes of binding sites. The higher affinity class had a Kd of 3.7 x 10(-10) M 3500 sites/platelet, while the lower affinity class had a Kd of 2.35 x 10(- 9) M and a capacity of 7500 sites/platelet. As with ristocetin-induced platelet agglutination, the carbohydrate content plays a significant role in the binding of the factor VIII/von Willebrand factor protein to the platelet.

Interactions of Purified Rat Factor VIII/von Willebrand Factor with Rat and Human Platelets – Effect of Albumin and Ristocetin

1984 ◽  
Vol 52 (01) ◽  
pp. 057-059 ◽  
Author(s):  
E Dejana ◽  
M Furlan ◽  
B Barbieri ◽  
M B Donati ◽  
E A Beck
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Rat Plasma ◽  
Human Platelets ◽  
High Concentrations ◽  
Low Sensitivity ◽  
Von Willebrand ◽  
Induced Aggregation ◽  
Willebrand Factor ◽  
Rat Platelets

SummaryRat platelets do not respond to ristocetin in their own plasma nor do they aggregate in the presence of bovine or porcine factor VIII von Willebrand factor (F VIII R:WF) or human F VIII R:WF in presence of ristocetin. However, rat plasma supports ristocetin induced aggregation of washed human platelets. In this study we report on purification of rat F VIII R:WF from cryoprecipitate. Similarly to porcine or bovine material, purified rat F VIII R:WF induced aggregation of human washed fixed platelets. This effect was enhanced by addition of ristocetin and was not modified by addition of albumin. Rat washed platelets were aggregated by ristocetin in the presence of rat or human F VIII R:WF provided that high concentrations of ristocetin are added in a system essentially free of extraneous proteins. Increasing concentrations of albumin dramatically reduced the ability of ristocetin to aggregate rat platelets while human platelet aggregation by human or rat F VIII R:WF was only moderately affected.These studies show that rat F VIII R:WF can interact with rat and human platelets. The lack of response of rat platelets to ristocetin in their own plasma is most likely due to a low sensitivity of rat platelets to this drug and to an inhibitory activity of plasma proteins on this reaction.

scholarly journals Characterization of human factor VIII and interaction with von Willebrand factor. An electron microscopic study

1990 ◽  
Vol 194 (2) ◽  
pp. 491-498 ◽  
Author(s):  
Harry F. G. HEIJNEN ◽  
Joost. A. KOEDAM ◽  
Helena SANDBERG ◽  
Nel H. BEESER-VISSER ◽  
Jan. W. SLOT ◽  
...  
Keyword(s):  
Factor Viii ◽  
Microscopic Study ◽  
Electron Microscopic Study ◽  
Von Willebrand Factor ◽  
Human Factor ◽  
Electron Microscopic ◽  
Human Factor Viii ◽  
Von Willebrand ◽  
Willebrand Factor

scholarly journals Effect of multimeric structure of the factor VIII/von Willebrand factor protein on binding to platelets

Blood ◽  
1981 ◽  
Vol 58 (2) ◽  
pp. 387-397 ◽  
Author(s):  
HR Gralnick ◽  
SB Williams ◽  
DK Morisato
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Competitive Inhibition ◽  
Human Platelets ◽  
Factor Vii ◽  
Variant Form ◽  
Factor Binding ◽  
Plasma Factor ◽  
Von Willebrand ◽  
Willebrand Factor

The characteristics of the intact factor VIII/von Willebrand factor protein binding to human platelets was compared to 2-mercaptoethanol- treated factor VIII/von Willebrand factor protein and to fractions of plasma factor VIII/von Willebrand factor protein that elute after the void volume. These studies indicate that the factor VIII/von Willebrand factor protein larger size oligomers bind preferentially with high affinity to low capacity sites on human platelets. The intermediate and smaller size oligomers bind with intermediate or low affinity to sites with a much greater capacity. The results from binding analysis are also paralleled by the competitive inhibition of the intact factor VIII/von Willebrand factor protein by the various 2-mercaptoethanol- treated materials. These studies indicate that the two classes of binding sites seen in previous reports of factor VII/von Willebrand factor binding reflect heterogeneity in the oligomer size of the factor VIII/von Willebrand factor protein used in these assays. This study provides a model for understanding some of the normal structure- function relationships of the normal factor VIII/von Willebrand factor protein and the defect(s) in a variant form of von Willebrand's disease. In this form of the disease, decreased factor VIII/von Willebrand factor binding to platelets is reflected in decreased von Willebrand factor activity but coagulant and/or antigen levels are normal or only slightly decreased.

Effect Of The Multimeric Structure Of The Factor VIII/Von Willebrand Factor Protein On Binding To Human Platelets

1981 ◽  
Author(s):  
H Gralnick ◽  
S Williams ◽  
D J Morisato
Keyword(s):  
Factor Viii ◽  
Von Willebrand Factor ◽  
Competitive Inhibition ◽  
High Capacity ◽  
Molecular Size ◽  
Human Platelets ◽  
Affinity Binding ◽  
Platelet Receptor ◽  
Von Willebrand ◽  
Willebrand Factor

We have studied the characteristics of binding of intact factor VIII/von Willebrand factor (f. VIII/vWf) protein and 2-mercaptoethanol (2ME) treated f. VIII/vWf protein to human platelets. The purified f. VIII/vWf was radiolabelled with tritiated 3H potassium borohydride; 4.5 × 103 molecules of the intact radiolabelled material bound per platelet. Of these some molecules bound with a high affinity/low capacity (Kd 0.21 nM and 1.5 × 103 molecules) and another with a low affinity/high capacity (Kd 2.5 nM and 3 × 103 molecules). When the material was reduced with 2ME at 0.01%, it bound with an intermediate affinity of 1.6 nM with a capacity of 4.0 × 103 and a low affinity binding of 12.5 nM and a capacity of 4.0 × 103 . The 0.1% 2ME-treated material revealed only low affinity binding with a Kd of 15 nM and the number of molecules bound 13 × 103. Studies of competitive inhibition of the intact f. VIII/vWf binding to human platelets by the reduced materials revealed that the smallest f. VIII/vWf protein (i.e., 0.1% 2ME) was the least effective while the 0.01% 2ME material was intermediate between the 0.1% and the intact material. The differences noted in the ability to displace the intact material as well as in binding to the human platelet were paralleled by decreases in the vWf activity of these proteins.These studies aid in our understanding of the binding of the f. VIII/vWf to platelets in that the binding sites on platelets may be homogeneous while the ligand is heterogenous. These studies reinforce the structure/function relationships of f. VIII/vWf proteins which have been defined using ristocetin-induced platelet aggregation (i.e., the minimum molecular size of the f. VIII/vWf protein and the penultimate galactose residues on the carbohydrate side chain). We conclude that these defects of the f. VIII/vWf protein also interfere with the protein binding to its platelet receptor and that f. VIII/vWf binding to platelets is an important primary step in hemostasis.

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