Prothrombin


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.

prothrombin

[prō′thräm·bən]
(biochemistry)
An inactive plasma protein precursor of thrombin. Also known as factor II; thrombinogen.

Prothrombin

 

(also factor II), in man and animals, a protein present in the blood plasma that is the primary component of the blood coagulation system.

Chemically, prothrombin is a glycoprotein composed of approximately 12 percent carbohydrates; the protein part of the molecule is in the form of one polypeptide chain. The molecular weight of prothrombin is approximately 70,000. Prothrombin is the precursor of the enzyme thrombin, which stimulates the formation of thrombi.

In an organism, prothrombin is activated into thrombin by prothrombinase, which is made up of phospholipid, Ca2+ ions, and coagulation factors V (accelerator globulin) and X (thrombokinase, autoprothrombin C). Factor X is a proteolytic enzyme and the active source of prothrombinase. Upon its conversion to thrombin, the prothrombin molecule loses approximately one-half of its former weight and three-quarters of its carbohydrate content.

The biosynthesis of prothrombin occurs in the cells of the liver and is regulated by vitamin K, which is produced by intestinal flora. In instances of vitamin K deficiency, the level of prothrombin in the blood drops below the normal level of 10 mg percent, often resulting in a tendency to bleed, which can manifest itself in early childhood hemorrhaging, obstructive jaundice, and certain diseases of the liver. It is believed that vitamin K deficiency causes the biosynthesis of anomalous molecules of prothrombin and reduces the ability of prothrombin to convert into thrombin. In medical practice, the prothrombin level is measured to determine the characteristics of an individual’s blood coagulation system (prothrombin index).

REFERENCE

Magnusson, S. “Thrombin and Prothrombin.” In The Enzymes, 3rd ed., vol. 3. New York-London, 1971.

I. P. BASKOVA

References in periodicals archive ?
Conclusion: The frequency of prothrombin gene mutation was found to be 4.
The association between prothrombin G20210A and arterial events is still controversial.
In the third cohort of two patients, one had very high liver enzymes and prothrombin time and she died within 24 hours of hospitalisation.
In addition there is a slower conversion of the mutant prothrombin to thrombin evidenced in clotting assays.
8-9 Modified Child-Turcotte-Pugh (MCTP) scoring system has scores for albumin, bilirubin, prothrombin time, ascites, and hepatic encephalopathy which are related to prognosis of stage.
In analyses adjusted for traditional cardiovascular risk factors and measures of vitamin K intake, a doubling of des-[gamma]-carboxy prothrombin concentration was associated with a 1.
31-36) Factor X is a critical coagulation factor in the common pathway, which serves to activate prothrombin to thrombin.
The diagnosis of factor VII deficiency is in the differential diagnosis of an isolated prolonged prothrombin time.
Platelet poor plasma was taken for estimation of prothrombin time and activated partial thromboplastin time with the help of coagulometer.
Genistein treatment upregulated prothrombin mRNA expression in HepG2 cells and this effect was amplified in the presence of the estrogen receptor expressed in Hep89 cells (pLess than0.
Factor V leiden and prothrombin G20210A variants, but not methylentetrahydrofolate reductase C677T, are associated with recurrent miscarriages.