Pastpapers for hemostasis (open Q) Flashcards by Christian Thorvaldsen

What kind of covalent bond is formed between thrombin and antithrombin ?

Ester bond between active Ser and the carboxylic group of the cleaved peptide bond on antithrombin

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Which is the cofactor in the thrombin catalyzed activation of F XIII

Fibrin (between fibrin alpha and gamma chain)

Ca2+ is also needed

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Write down the substrates and products of the reaction catalyzed by FXIII a (Name the amino acids in the substrates and the name of the formed bond)

Substrate: lysine and glutamine side chains in gamma and alpha chains of fibrin
Product: gamma-glutamyl-lysine isopeptide and ammonia

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What kind of covalent bond is formed between thrombin and α2-macroglobulin ?

isopeptide bond between an ε–amino group of Lys on thrombin and a carboxylic group from a Gln-Cys thioester bond in α2-macroglobulin

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Which proteases are necessary for the destruction of the intrinsic tenase and the prothrombinase complexes ?

Thrombin (for the activation of protein C) and activated protein C for the inactivaiton of factor 5a and 8a

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Which protein cofactors are necessary for the destruction of the intrinsic tenase and the prothrombinase complexes ?

Thrombomodulin, protein S

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What is the mode of action of streptokinase?

Forms a complex with human plasminogen, in which plasminogen gains activity as plasminogen activator.
Increased fibrinolytic activity

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List two distinct functions of von Willebrand factor

Barrier of F VIII, mediator of platelet adhesion at high shear stress

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What is the mode of antithrombolytic action of TAFI (Thrombin activatable fibrinolysis inhibitor) ?

Cleaves C-terminal Lys residues and decreases the binding sites for tPA and plasminogen in fibrin and moderates the cofactor of fibrin in plasminogen activation

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How is the formation of blood coagulation inhibited in the clinic?

By Heparin, Vitamin K Antagonists- Coumarins (Marevan, Warfarin)

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What activates Protein C?

Thrombin in complex with thrombomodulin

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How is Plasmin formed?

From Plasminogen in the presence of Plasminogen activators.

A plasminogen activator is a serine protease which converts plasminogen to plasmin, thus promoting fibrinolysis. 2 types: tPA and uPA. Inhibited by plasminogen activator inhibitor-1 and plasminogen activator inhibitor-2.

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How is fibrinolysis terminated?

Alpha2- antiplasmin
Alpha2- macroglobulin
Plasmin activator inhibiting factor 1+2

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At least one drug inhibiting platelet activation

ASPIRIN inhibits COX1 irreversibly (converting AA to TXA2)

ADP receptor inhibitors

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Is it possible that thrombin exhibits any antithrombic effect?

Yeah baby! The thrombim-thrombomodulin complex activates Protein C, which inhibits Factor Va + VIIIa

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Background of activated Protein C resistance

The inability of Protein C to cleave Va and VIIIa, leads to hypercoagulability.

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Which diagnostic assay is based on the intrinsic pathway?

PTT- Partial Thromboplastin Time (Kaoulin cephalin clotting time) To detect Vit K def., vW disease, hemophilia, Hagmann factor defiency

Kinetic significance of the phospholipid bound complexes in blood coagulation?

Increase the reaction rate between the involved factors 250 000x

Where is not tissue factor present under physiologic conditions?

Healthy endothelial cells

Blood

How can tPA be increased?

In presence of a cofactor, which might be fibrin

Primary thrombin inhibitor in blood? How is effect enhanced pharmacologically?

Antithrombin.

By the addition of heparin.

List at least 3 triggers of platelet activation

Primary activators:
Collagen
Thrombin
Platelet-activating factor (PAF)
Secondary activators:
ADP
TXA2
Serotonin

What initiates the blood coagulation at sites of injury?

Tissue factor with factor 7a

What types of plasminogen activators are used in thrombolytic therapy?

1: tPA (Tissue type Plasminogen activators)
2: uPA (Urokinase Plasminogen activators)
3: Streptokinase

How does Hirudin act?

Its a type of a "direct thrombin inhibitors". Its an inhibitor of THROMBIN (direct without the need of a cofactor) by binding to exosite 1 and active site. Has a negatively charged tail, it binds to active site of thrombin and inactivates it. (it has a specific activity on fibrinogen) Hirudin prevent formation of blood clots & thrombus, do not interfere with ability of serum proteins. Binds to both fibrin-bound and soluble thrombin

1. Describe composition of prothrombinase complex | 2. What are the structurally important elements of complex formation

1. composed by activated factor X and V | 2. These factors are bound by Ca-ions to the negative phospholipid membrane

What are the substrates for thrombin in blood coagulation system?

Fibrinogen (factor 2) Factor 5, 8, 11, 13 PAR-receptor Binds to thrombomodulin along with calcium to activate protein C.

Enzymes that degrades fibrin clots?

Plasmin

Role of Platelets

First, platelets stick to exposed collagen of the subendothelial layer: adhesion. Second, they change shape, turn on receptors and secrete chemical messengers (ADP, Vwf, thrombin, PDGF): activation. Third, they stick to each other: aggregation. Formation of this platelet plug (primary hemostasis) is followed by activation of the coagulation cascade with resultant fibrin deposition and linking (secondary hemostasis).

Purpose of phospholipids on platelets membrane

Complex formaiton for tenase and prothrombinase complexes. This complexes enhance its activity 250 000x! Phosphatidylserine with its negative charge can be used as a building block with Ca2+, cofactors, substrate and enzyme.

Leiden mutation

Inherited disorder of blood clotting, activated protein C resistance. It results in a factor V variant that cannot be easily degraded by activated protein C.

Effect of Coumarin (Warfarin); after how much time is the effect of coumarin observable?

a. Coumarin inhibits Vit K Epoxide Reductase which is responsible for Glu to Gla change of factors 2, 7, 9, 10 b. not an observable effect; it takes about a day to see the effects.

Substrates of factor VII

Exposure of factor tissue factor (cofactor), which binds VIIa, causing activation of X -> Xa + through the alternative pathway, activation of factor 9

How does endothelia cell initiate coagulation formation?

Damaged endothelium does not secrete the same amount of antithrombotic substances. Exposure of the extravascular matrix (E.g. Collagen and vWF) will cause platelet adherence and activaiton.

What is the mechanism of action of heparin?

Heparin binds to exosite 2 on thrombin. This increase its affinity to antithrombin which leads to more thrombin removal.

What is the role of the primary cilium of endothelial cells?

Shear stress -> Ca2+ -> NO production -> vasodilation

Which component forms a secondary matrix in thrombi in addition ot fibrin?

Neutrophil extracellular trap (NET)

Write down the targets of TFPI in the order of their binding

1: 10a 2: 7a with TF (in complex)

List the three major targets of thrombin in the positive feed-back loops in blood plasma

5, 8, 11

Function of alpha1-protease inhibitor (alpha1-antitrypsin)

Inactivated almost all serine proteases (e.g. thrombin and plasmin. Equimolar complexes.