thrombin

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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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

thrombin

[′thräm·bən] (biochemistry) An enzyme elaborated from prothrombin in shed blood which induces clotting by converting fibrinogen to fibrin.

thrombin

[throm´bin] 1. the activated form of coagulation factor II (prothrombin), which catalyzes the conversion of fibrinogen to fibrin.2. a preparation of this compound prepared from prothrombin of bovine origin, used as a topical hemostatic.thrombin time (TT) the time required for plasma fibrinogen to form thrombin: exogenous thrombin is added to citrated plasma and the time to clot formation is measured. Prolonged TT is seen with abnormalities of fibrinogen and in the presence of heparin or degradation products of fibrin or fibrinogen.

throm·bin

(throm'bin), 1. An enzyme (proteinase), formed in shed blood, that converts fibrinogen into fibrin by hydrolyzing peptides (and amides and esters) of l-arginine; formed from prothrombin by the action of prothrombinase (factor Xa, another proteinase). 2. A sterile protein substance prepared from prothrombin of bovine origin through interaction with thromboplastin in the presence of calcium; causes clotting of whole blood, plasma, or a fibrinogen solution; used as a topical hemostatic for capillary bleeding with or without fibrin foam in general and plastic surgical procedures. Synonym(s): factor IIa, fibrinogenase, thrombase, thrombosin

thrombin

(thrŏm′bĭn)n. A protease in blood that facilitates blood clotting by converting fibrinogen to fibrin.

thrombin

Hematology A key clot promoting enzyme that converts fibrinogen to fibrin and protects against fibrinolysis by activating thrombin-activatable fibrinolysis inhibitor. See Fibrin, Fibrinolysis, TAFI.

throm·bin

(throm'bin) 1. An enzyme (proteinase), formed in shed blood, that converts fibrinogen into fibrin by hydrolyzing peptides (and amides and esters) of l-arginine; formed from prothrombin by the action of prothrombinase (factor Xa, another proteinase). 2. A sterile protein substance prepared from prothrombin of bovine origin through interaction with thromboplastin in the presence of calcium; causes clotting of whole blood, plasma, or a fibrinogen solution; used as a topical hemostatic for capillary bleeding with or without fibrin foam in general and plastic surgical procedures.
Synonym(s): factor IIa.

thrombin

An enzyme in the blood that converts fibrinogen to fibrin, thus forming a blood clot.

thrombin

see BLOOD CLOTTING.

Thrombin

Thrombin is a protein produced by the body. It is a specific clotting factor that plays an important role in the blood clotting process.Mentioned in: Anticoagulant and Antiplatelet Drugs, Fibrinogen Test, Prothrombin Time

throm·bin

(throm'bin) 1. An enzyme (proteinase), formed in shed blood, which converts fibrinogen into fibrin by hydrolyzing peptides (and amides and esters) of l-arginine; formed from prothrombin by the action of prothrombinase. 2. A sterile protein substance prepared from prothrombin of bovine origin through interaction with thromboplastin in the presence of calcium; causes clotting; used as a topical hemostatic for capillary bleeding in general and plastic surgical procedures.
Synonym(s): factor IIa.

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REFERENCES

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Words related to thrombin

noun an enzyme that acts on fibrinogen in blood causing it to clot

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