thrombin


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Related to thrombin: antithrombin, Thrombin time

thrombin:

see blood clottingblood clotting,
process by which the blood coagulates to form solid masses, or clots. In minor injuries, small oval bodies called platelets, or thrombocytes, tend to collect and form plugs in blood vessel openings.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Thrombin

 

an enzyme of the hydrolase class, a major element in the blood-clotting system of man and animals. It is present in blood in the form of the inactive precursor prothrombin and is activated by prothrombinase, or active thromboplastin. Chemically, thrombin is a glycoprotein with a molecular weight of about 40,000; it contains about 5 percent carbohydrate.

Thrombin was isolated in crystalline form in 1972 by the American physiologist W. Seegers and his associates. It is similar in primary and tertiary structure to the serine proteolytic enzymes such as trypsin. A thrombin molecule consists of two polypeptide chains linked by a disulfide bond. The A chain of bovine thrombin contains 49 amino acid radicals, and the B chain, 265 radicals. The active center of the enzyme, as well as the carbohydrate constituent, are located in the B chain. Thrombin exists in several active forms, which differ in the structure of the B chain.

The main function of thrombin is to convert fibrinogen into fibrin. Thrombin hydrolyzes four arginyl-glycine bonds in the fibrinogen molecule. Four peptides then split off to form a fibrin monomer, which becomes polymerized into the fibrin clot that is the basis of a thrombus. The reactions of limited proteolysis with the participation of thrombin are accompanied by the activation of Factor XIII (fibrin stabilizing factor) and of Factors V and VIII, which take part in the reactions of the internal blood-clotting mechanism. Thrombin aids in platelet aggregation and in clot retraction. A relative excess of thrombin in the body has been shown to automatically initiate the activity of the anticoagu-lating system. This is accompanied by the introduction of heparin and the activator of plasminogen into the bloodstream, substances that help maintain the blood’s liquid state.

Thrombin is inactivated by diisopropyl fluorophosphate, which blocks the hydroxyl group of serine that enters the active center, and by other inhibitors characteristic of the serine proteinase group. Thrombin is inactivated in blood by the plasma antithrombins α2-macroglobulin, antithrombin III, and/or heparin. A specific nonplasma thrombin inhibitor is the polypeptide hirudin, found in the buccal glands of leeches.

Thrombin is used to arrest capillary bleeding by the application of fibrin foam soaked in thrombin to the affected surface.

REFERENCES

Magnusson, S. “Thrombin and Prothrombin.” In The Enzymes, 3rd ed., vol. 3. New York–London, 1971.
“A New Thrombin: Purification, Aminoacid Composition, and Crystallization.” Thrombosis Research, 1972, vol. 1, p. 533.

I. P. BASKOVA

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

thrombin

[′thräm·bən]
(biochemistry)
An enzyme elaborated from prothrombin in shed blood which induces clotting by converting fibrinogen to fibrin.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Experimental group: 500 mg fat tissue; 0.60 cc thrombin combined Group (1\2)
(25.)Boffa MB, Nesheim ME, Koschinsky ML Thrombin activable fibrinolysis inhibitor (TAFI) molecular genetics of an emerging potential risk factor for thrombotic disorders Curr Drug Targets Cardiovasc Haematol Disord 2001, 1 59-74.
First, an average of four thrombin molecules was attached to a flat DNA scaffold.
Thrombin is a proven blood coagulation agent--used on its own or in combination with other hemostats--estimated to be used in over 1 million patients per year in the United States to help surgeons address intraoperative bleeding.' RECOTHROM is a thrombin-based product indicated as an aid to hemostasis whenever oozing blood and minor bleeding from capillaries and small venules is accessible and control of bleeding by standard surgical techniques is ineffective or impractical in adults and pediatric populations greater than or equal to one month of age.
Thrombin and its inactive precursor prothrombin have been also detected in the brain [24,25].
Soft tissue ultrasound after the two thrombin injections showed pseudoaneurysm and a 7 x 3.3 x 4 cm multilobular hematoma at the base of the right neck.
The current antithrombotic therapies include heparin (unfractionated heparin and low-molecular-weight heparins), fondaparinux, vitamin K antagonists, factor Xa inhibitors, and direct thrombin inhibitors [6].
The first folding-based GQ electrochemical biosensor for thrombin was prepared by covalently attaching methylene blue (MB) labelled TBA sequences d(T[A.sub.2]G[T.sub.2]CATCT[C.sub.4][G.sub.2][T.sub.2][G.sub.2]TGT[G.sub.2][T.sub.2] [G.sub.2]T) [93] and d([T.sub.2][C.sub.2][A.sub.2]C[G.sub.2][T.sub.2][G.sub.2]TGT[G.sub.2][T.sub.2][G.sub.2]) [94] to gold electrode surfaces.
(11) The thrombin time (TT) is usually normal; however, when the patient has been exposed to bovine thrombin, it can be prolonged.
We believe that the evidence for thrombin as one of the main proteases for cTnT degradation is convincing.
In view of deranged renal function CT angiogram was not done and decision was made to treat the pseudoaneurysm with percutaneous thrombin injection.
The mutant prothrombins were shown to have reduced activity in clotting assays and the produced thrombin was markedly resistant to inhibition by antithrombin.