Prothrombin (factor II, trombogen) - glycoproteid, present in plasma and is the precursor of thrombin - the enzymethat causes blood clotting. In normal plasma contains 10-20 mg% of prothrombin. The synthesis of protrombina occurs in the liver and is dependent on the availability of vitamin K. the lack of this vitamin that occurs, for example, in obstructive jaundice appears spontaneous bleeding caused by the violation of the synthesis of protrombina. Gipoprotrombinemii may develop early children haemorrhage. To determine the levels of prothrombin in the plasma measure the so-called prothrombin time (see). Lowering the concentration of prothrombin to 30-25% of the norm there has been a sharp increase in the duration of bleeding and spontaneous hemorrhages. In this case, the person is given a vitamin K.
Cm. also the Clotting of blood.

Prothrombin (synonym: factor II, trombogen) - inactive precursor of the enzyme thrombin in the blood plasma.
Prothrombin is glikoproteinom; it comes from 4.3 to 9.6% carbohydrates (hexoses, pentoses, sialic acids, hexosamine). Prothrombin contains 66,12%, 6.5% Of N, 13,5% N 0,96% S and 3.75% ash. In Petrograd found 18 amino acids with a predominance of glutamine, aspartic, arginine, lysine. Mol. weight P. equal 62 700-68 000. Electrophoretic on, are not homogeneous, the main part corresponds A2-globulin. Turning point fall in the thrombin is carried out under the action of tissue or blood thromboplastin in the presence of calcium ions or when you activate salts (a 25% solution of sodium citrate). P. fairly stable and is not destroyed when heated to 56 degrees for 2 hours.
During blood coagulation almost all of the prothrombin turns into thrombin.
In normal plasma contains from 10 to 20 mg% P. the Content P. changing: it is elevated during pregnancy and menstruation, after loss of blood, when hyperventilation of the lungs and reduced in newborns, and also after meal, in hemorrhagic shock after administration of salicylates and sulfanilamidam, diseases of the liver. The synthesis of protrombina is microsomes parenchymal liver cells and depends on the presence in the body of vitamin K. In case of insufficiency of vitamin K, caused by violation of his suction (obstructive jaundice, malignancy), or parenchymal liver (cirrhosis, liver atrophy, decompensated heart diseases with congestion in the liver) is developing acute gipoprotrombinemiey and it caused the bleeding. Indirect anticoagulants (dikumarina, fenilin and other inhibit the synthesis P. and called through 12-24 hours after ingestion by lower concentrations of prothrombin in the blood. To determine P. in blood use a variety of methods; the most popular method of Quick, consisting in the determination of clotting time oxalate plasma in the presence of excess tissue thromboplastin and optimum quantity of calcium chloride.