Factor X

  • OMIM: 227600
  • UniProt: P00742
  • MGI: 103107

Stuart - Prower factor (also Thrombokinase or factor X) is an enzyme involved in blood clotting ( serine ). Therefore it is included in the group of coagulation factors. Its EC number is, so it belongs to the serine proteases. Stuart - Prower factor has a molecular mass of 59 kDa and is synthesized in the liver, to vitamin K is needed. It belongs to the group of α - globulins, and consists of one heavy and one light chain. Its half-life in blood is 40 to 45 hours, its plasma concentration 7-10 mg / l


The gene of the Stuart - Prower factor is q34 on chromosome 13 locus in humans.


Upon activation of Stuart Prower factor peptide bond in the heavy chain carrying the active site cleft. This can be activated in two different ways. The extrinsic pathway, which occurs when blood vessels are damaged, activates a complex of activated proconvertin (factor VIIa ), and tissue factor ( factor III), Stuart - Prower factor ( factor Xa). In contrast, it is the intrinsic pathway, which occurs when parts of the clotting cascade to negatively charged particles meet (such as collagen under the endothelium ) of a complex of the activated Christmas factor ( factor IX ) and antihemophilic globulin A ( factor VIIIa) enabled. It can also be activated by the digestive enzyme trypsin and the venom of Russell 's viper.

Factor Xa is therefore the first step of the coagulation phase, everything before is part of the activation phase. He cleaves prothrombin (factor II) at two locations ( between Arg -Thr bond and between an Arg -Ile bond). This converts prothrombin into thrombin. For this process, the Stuart - Prower factor requires activated Proaccelerin (factor Va) as a cofactor.

Factor Xa is inactivated by a protein Z -dependent serine proteinase. The affinity of this enzyme for factor Xa is a thousand-fold by protein Z. Defective protein Z leads to an increased activity of the Stuart - Prower factor and a slope for the formation of thrombosis.


Congenital factor X defects are rare ( 1:500,000 ) and contact with nasal bleeding ( epistaxis), bleeding into joints ( hemarthrosis ) and blood loss in the digestive tract (gastrointestinal bleeding ) on. Regardless of congenital defects, a reduced incidence of Stuart - Prower factor occur in various diseases.

A lack of vitamin K or its inhibition by warfarin or similar antagonists leads to the formation of inactive factor X. In warfarin therapy this effect in preventing thrombosis is desired.


Factor X is present as a concentrate in frozen blood plasma and in the prothrombin complex. The only approved factor X factor concentrate is XP Behring, manufactured by CSL Behring.

History of Research

The factor X deficiency was of British (C. Hougie et al. ), German (M. Horder ) and Swiss ( K.-D. Bachmann et al. ) Researchers independently discovered and described in 1957 and 1958. As with other clotting factors as well, the factor X has been designated for those patients in which a defect has been first described. The nomenclature comes from the Swiss Working Group for K.-D. Bachmann.