|, PT, RPRGL2, THPH1, coagulation factor II, thrombin|
Thrombin (EC 184.108.40.206, fibrinogenase, thrombase, thrombofort, topical, thrombin-C, tropostasin, activated blood-coagulation factor II, blood-coagulation factor IIa, factor IIa, E thrombin, beta-thrombin, gamma-thrombin) is a serine protease, an enzyme that, in humans, is encoded by the F2 gene.Prothrombin (coagulation factor II) is proteolytically cleaved to form thrombin in the clotting process. Thrombin in turn acts as a serine protease that converts soluble fibrinogen into insoluble strands of fibrin, as well as catalyzing many other coagulation-related reactions.
After the description of fibrinogen and fibrin, Alexander Schmidt hypothesised the existence of an enzyme that converts fibrinogen into fibrin in 1872.
Prothrombin was discovered by Pekelharing in 1894.
Thrombin is produced by the enzymatic cleavage of two sites on prothrombin by activated Factor X (Xa). The activity of factor Xa is greatly enhanced by binding to activated Factor V (Va), termed the prothrombinase complex. Prothrombin is produced in the liver and is co-translationally modified in a vitamin K-dependent reaction that converts 10-12 glutamic acids in the N terminus of the molecule to gamma-carboxyglutamic acid (Gla).In the presence of calcium, the Gla residues promote the binding of prothrombin to phospholipid bilayers. Deficiency of vitamin K or administration of the anticoagulant warfarin inhibits the production of gamma-carboxyglutamic acid residues, slowing the activation of the coagulation cascade.
In human adults, the normal blood level of antithrombin activity has been measured to be around 1.1 units/mL. Newborn levels of thrombin steadily increase after birth to reach normal adult levels, from a level of around 0.5 units/mL 1 day after birth, to a level of around 0.9 units/mL after 6 months of life.
In the blood coagulation pathway, thrombin acts to convert factor XI to XIa, VIII to VIIIa, V to Va, fibrinogen to fibrin, and XIII to XIIIa. In the conversion of fibrinogen into fibrin, thrombin catalyzes the cleavage of fibrinopeptides A and B from the respective Aα and Bβ chains of fibrinogen to form fibrin monomers.
Factor XIIIa is a transglutaminase that catalyzes the formation of covalent bonds between lysine and glutamine residues in fibrin. The covalent bonds increase the stability of the fibrin clot. Thrombin interacts with thrombomodulin.
As part of its activity in the coagulation cascade, thrombin also promotes platelet activation and aggregation via activation of protease-activated receptors on the cell membrane of the platelet.
Thrombin bound to thrombomodulin activates protein C, an inhibitor of the coagulation cascade. The activation of protein C is greatly enhanced following the binding of thrombin to thrombomodulin, an integral membrane protein expressed by endothelial cells. Activated protein C inactivates factors Va and VIIIa. Binding of activated protein C to protein S leads to a modest increase in its activity. Thrombin is also inactivated by antithrombin, a serine protease inhibitor.
The molecular weight of prothrombin is approximately 72,000 Da. The catalytic domain is released from prothrombin fragment 1.2 to create the active enzyme thrombin, which has a molecular weight of 36,000 Da. Structurally, it is a member of the large PA clan of proteases.
Prothrombin is composed of four domains; an N-terminal Gla domain, two kringle domains and a C-terminal trypsin-like serine protease domain. Factor Xa with factor V as a cofactor leads to cleavage of the Gla and two Kringle domains (forming together a fragment called fragment 1.2) and leave thrombin, consisting solely of the serine protease domain.
As is the case for all serine proteases, prothrombin is converted to active thrombin by proteolysis of an internal peptide bond, exposing a new N-terminal Ile-NH3. The historic model of activation of serine proteases involves insertion of this newly formed N-terminus of the heavy chain into the β-barrel promoting the correct conformation of the catalytic residues.Contrary to crystal structures of active thrombin, hydrogen-deuterium exchange mass spectrometry studies indicate that this N-terminal Ile-NH3 does not become inserted into the β-barrel in the apo form of thrombin. However, binding of the active fragment of thrombomodulin appears to allosterically promote the active conformation of thrombin by inserting this N-terminal region.
The thrombin (prothrombin) gene is located on the eleventh chromosome (11p11-q12).
There are an estimated 30 people in the world that have been diagnosed with the congenital form of Factor II deficiency,which should not be confused with the prothrombin G20210A mutation, which is also called the factor II mutation. Prothrombin G20210A is congenital.
Prothrombin G20210A is not usually accompanied by other factor mutations (i.e., the most common is factor V Leiden). The gene may be inherited heterozygous (1 pair), or much more rarely, homozygous (2 pairs), and is not related to gender or blood type. Homozygous mutations increase the risk of thrombosis more than heterozygous mutations, but the relative increased risk is not well documented. Other potential risks for thrombosis, such as oral contraceptives may be additive. The previously reported relationship of inflammatory bowel disease (i.e., Crohn's disease or ulcerative colitis) and prothrombin G20210A or factor V Leiden mutation have been contradicted by research.
Activation of prothrombin is crucial in physiological and pathological coagulation. Various rare diseases involving prothrombin have been described (e.g., hypoprothrombinemia). Anti-prothrombin antibodies in autoimmune disease may be a factor in the formation of the lupus anticoagulant (also known as antiphospholipid syndrome). Hyperprothrombinemia can be caused by the G20210A mutation.
Thrombin, a potent vasoconstrictor and mitogen, is implicated as a major factor in vasospasm following subarachnoid hemorrhage. Blood from a ruptured cerebral aneurysm clots around a cerebral artery, releasing thrombin. This can induce an acute and prolonged narrowing of the blood vessel, potentially resulting in cerebral ischemia and infarction (stroke).
Beyond its key role in the dynamic process of thrombus formation, thrombin has a pronounced pro-inflammatory character, which may influence the onset and progression of atherosclerosis. Acting via its specific cell membrane receptors (protease activated receptors: PAR-1, PAR-3 and PAR-4), which are abundantly expressed in all arterial vessel wall constituents, thrombin has the potential to exert pro-atherogenic actions such as inflammation, leukocyte recruitment into the atherosclerotic plaque, enhanced oxidative stress, migration and proliferation of vascular smooth muscle cells, apoptosis and angiogenesis.
Thrombin is implicated in the physiology of blood clots. Its presence indicates the existence of a clot. In 2013 a system for detecting the presence of thrombin was developed in mice. It combines peptide-coated iron oxide attached to "reporter chemicals". When a peptide binds to a thrombin molecule, the report is released and appears in the urine where it can be detected. Human testing has not been conducted.
Due to its high proteolytic specificity, thrombin is a valuable biochemical tool. The thrombin cleavage site (Leu-Val-Pro-Arg-Gly-Ser) is commonly included in linker regions of recombinant fusion protein constructs. Following purification of the fusion protein, thrombin can be used to selectively cleave between the arginine and glycine residues of the cleavage site, effectively removing the purification tag from the protein of interest with a high degree of specificity.
Prothrombin complex concentrate and fresh frozen plasma are prothrombin-rich coagulation factor preparations that can be used to correct deficiencies (usually due to medication) of prothrombin. Indications include intractable bleeding due to warfarin.
Manipulation of prothrombin is central to the mode of action of most anticoagulants. Warfarin and related drugs inhibit vitamin K-dependent carboxylation of several coagulation factors, including prothrombin. Heparin increases the affinity of antithrombin to thrombin (as well as factor Xa). The direct thrombin inhibitors, a newer class of medication, directly inhibit thrombin by binding to its active site.
Recombinant thrombin is available as a powder for reconstitution into aqueous solution. It can be applied topically during surgery, as an aid to hemostasis. It can be useful for controlling minor bleeding from capillaries and small venules, but ineffective and not indicated for massive or brisk arterial bleeding.
Thrombin, combined with fibrinogen, is sold under the brand name Fibrimex for use as a binding agent for meat. Both proteins in Fibrimex derives from porcine or bovine blood.According to the manufacturer it can be used to produce new kinds of mixed meats (for example combining beef and fish seamlessly). The manufacturer also states that it can be used to combine whole muscle meat, form and portion these, thus cutting down on production costs without a loss in quality.
General secretary Jan Bertoft of Swedish Consumers' Association has stated that "there is danger of misleading the consumers since there is no way to tell this reconstituted meat from real meat".
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism of coagulation involves activation, adhesion and aggregation of platelets, as well as deposition and maturation of fibrin.
Disseminated intravascular coagulation (DIC) is a condition in which blood clots form throughout the body, blocking small blood vessels. Symptoms may include chest pain, shortness of breath, leg pain, problems speaking, or problems moving parts of the body. As clotting factors and platelets are used up, bleeding may occur. This may include blood in the urine, blood in the stool, or bleeding into the skin. Complications may include organ failure.
Fibrinogen is a glycoprotein complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood clot. Fibrin clots function primarily to occlude blood vessels to stop bleeding. Fibrin also binds and reduces the activity of thrombin. This activity, sometimes referred to as antithrombin I, limits clotting. Fibrin also mediates blood platelet and endothelial cell spreading, tissue fibroblast proliferation, capillary tube formation, and angiogenesis and thereby promotes revascularization and wound healing.
Antithrombin (AT) is a small glycoprotein that inactivates several enzymes of the coagulation system. It is a 432-amino-acid protein produced by the liver. It contains three disulfide bonds and a total of four possible glycosylation sites. α-Antithrombin is the dominant form of antithrombin found in blood plasma and has an oligosaccharide occupying each of its four glycosylation sites. A single glycosylation site remains consistently un-occupied in the minor form of antithrombin, β-antithrombin. Its activity is increased manyfold by the anticoagulant drug heparin, which enhances the binding of antithrombin to factor IIa (Thrombin) and factor Xa.
Factor XIII or fibrin stabilizing factor is a zymogen found in blood of humans and some other animals. It is activated by thrombin to factor XIIIa. Factor XIIIa is an enzyme of the blood coagulation system that crosslinks fibrin. Deficiency of XIII worsens clot stability and increases bleeding tendency.
Protein C, also known as autoprothrombin IIA and blood coagulation factor XIX, is a zymogen, that is, an inactive enzyme. The activated form plays an important role in regulating anticoagulation, inflammation, and cell death and maintaining the permeability of blood vessel walls in humans and other animals. Activated protein C (APC) performs these operations primarily by proteolytically inactivating proteins Factor Va and Factor VIIIa. APC is classified as a serine protease since it contains a residue of serine in its active site. In humans, protein C is encoded by the PROC gene, which is found on chromosome 2.
Thrombophilia is an abnormality of blood coagulation that increases the risk of thrombosis. Such abnormalities can be identified in 50% of people who have an episode of thrombosis that was not provoked by other causes. A significant proportion of the population has a detectable thrombophilic abnormality, but most of these develop thrombosis only in the presence of an additional risk factor.
Factor X, also known by the eponym Stuart–Prower factor, is an enzyme of the coagulation cascade. It is a serine endopeptidase. Factor X is synthesized in the liver and requires vitamin K for its synthesis.
Factor V is a protein of the coagulation system, rarely referred to as proaccelerin or labile factor. In contrast to most other coagulation factors, it is not enzymatically active but functions as a cofactor. Deficiency leads to predisposition for hemorrhage, while some mutations predispose for thrombosis.
Hirudin is a naturally occurring peptide in the salivary glands of blood-sucking leeches that has a blood anticoagulant property. This is fundamental for the leeches’ habit of feeding on blood, since it keeps a host's blood flowing after the worm's initial puncture of the skin.
Plasminogen activators are serine proteases that catalyze the activation of plasmin via proteolytic cleavage of its zymogen form plasminogen. Plasmin is an important factor in fibrinolysis, the breakdown of fibrin polymers formed during blood clotting. There are two main plasminogen activators: urokinase (uPA) and tissue plasminogen activator (tPA). Tissue plasminogen activators are used to treat medical conditions related to blood clotting including embolic or thrombotic stroke, myocardial infarction, and pulmonary embolism.
Tissue factor, also called platelet tissue factor, factor III, or CD142, is a protein encoded by the F3 gene, present in subendothelial tissue and leukocytes. Its role in the clotting process is the initiation of thrombin formation from the zymogen prothrombin. Thromboplastin defines the cascade that leads to the activation of factor X—the tissue factor pathway. In doing so, it has replaced the previously named extrinsic pathway in order to eliminate ambiguity.
The prothrombinase complex consists of the serine protease, Factor Xa, and the protein cofactor, Factor Va. The complex assembles on negatively charged phospholipid membranes in the presence of calcium ions. The prothrombinase complex catalyzes the conversion of prothrombin (Factor II), an inactive zymogen, to thrombin (Factor IIa), an active serine protease. The activation of thrombin is a critical reaction in the coagulation cascade, which functions to regulate hemostasis in the body. To produce thrombin, the prothrombinase complex cleaves two peptide bonds in prothrombin, one after Arg271 and the other after Arg320. Although it has been shown that Factor Xa can activate prothrombin when unassociated with the prothrombinase complex, the rate of thrombin formation is severely decreased under such circumstances. The prothrombinase complex can catalyze the activation of prothrombin at a rate 3 x 105-fold faster than can Factor Xa alone. Thus, the prothrombinase complex is required for the efficient production of activated thrombin and also for adequate hemostasis.
The thrombin time (TT), also known as the thrombin clotting time (TCT) is a blood test that measures the time it takes for a clot to form in the plasma of a blood sample containing anticoagulant, after an excess of thrombin has been added. It is used to diagnose blood coagulation disorders and to assess the effectiveness of fibrinolytic therapy. This test is repeated with pooled plasma from normal patients. The difference in time between the test and the 'normal' indicates an abnormality in the conversion of fibrinogen to fibrin, an insoluble protein.
Protein C inhibitor is a serine protease inhibitor (serpin) that limits the activity of protein C.
Batroxobin, also known as reptilase, is a snake venom enzyme with Venombin A activity produced by Bothrops atrox and Bothrops moojeni, venomous species of pit viper found east of the Andes in South America. It is a hemotoxin which acts as a serine protease similarly to thrombin, and has been the subject of many medical studies as a replacement of thrombin. Different enzymes, isolated from different species of Bothrops, have been called batroxobin, but unless stated otherwise, this article covers the batroxobin produced by B. moojeni, as this is the most studied variety.
Blood clotting tests are the tests used for diagnostics of the hemostasis system. Coagulometer is the medical laboratory analyzer used for testing of the hemostasis system. Modern coagulometers realize different methods of activation and observation of development of blood clots in blood or in blood plasma.
Four drugs from the class of direct Xa inhibitors are marketed worldwide. Rivaroxaban (Xarelto) was the first approved FXa inhibitor to become commercially available in Europe and Canada in 2008. The second one was apixaban (Eliquis), approved in Europe in 2011 and in the United States in 2012. The third one edoxaban was approved in Japan in 2011 and in Europe and the US in 2015. Betrixaban (Bevyxxa) was approved in the US in 2017.
The platelet plug, also known as the hemostatic plug or platelet thrombus, is an aggregation of platelets formed during early stages of hemostasis in response to one or more injuries to blood vessel walls. After platelets are recruited and begin to accumulate around the breakage, their “sticky” nature allows them to adhere to each other. This forms a platelet plug, which prevents more blood from leaving the body as well as any outside contaminants from getting in. The plug provides a temporary blockage of the break in the vasculature. As such, platelet plug formation occurs after vasoconstriction of the blood vessels but before the creation of the fibrin mesh clot, which is the more permanent solution to the injury. The result of the platelet plug formation is the coagulation of blood. It can also be referred to as primary hemostasis.
The fibrinopeptides, fibrinopeptide A (FpA) and fibrinopeptide B (FpB), are peptides which are located in the central region of the fibrous glycoprotein fibrinogen and are cleaved by the enzyme thrombin to convert fibrinogen into covalently-linked fibrin monomers. The N-terminal FpA is cleaved from the Aα chains of fibrinogen and FpB from the Bβ chains of fibrinogen, with FpA released before FpB. Subsequent to their formation, fibrin monomers are converted to cross-linked fibrin polymers by the action of thrombin-activated factor XIII, and these fibrin polymers form the backbone of a thrombus. Hence, the fibrinopeptides are sensitive markers of fibrinogenesis, thrombin activity, and coagulation.