What is factor X?

Updated: Feb 06, 2020
  • Author: George Ansstas, MD; Chief Editor: Eric B Staros, MD  more...
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Factor X is synthesized in the liver, and vitamin K is required for its production. The gene for human factor X is on a chromosome in close proximity to the factor VII gene. [2, 5] Factor X has a molecular weight of 59,000 daltons with a plasma half-life of approximately 34-40 hours. [2] Complete deficiency of factor X resulted either in intrauterine death or fatal hemorrhage within 5 days after birth in a mouse model. [6]

Factor X is activated to fully active factor Xa by factor VIIa/TF or factor IXa/VIIIa. Factor Xa in complex with factor Va (termed the prothrombinase complex) on a phospholipid membrane surface activates prothrombin to thrombin by cleaving two peptide bonds. Factor Xa may also play a physiologic role in activation of factors VII, [7] VIII, [8] and V. [9] Although any membrane surface that expresses anionic phospholipid can support prothrombinase complex assembly, the activated platelet surface is especially well suited for this purpose. Prothrombinase assembly on platelets is not strictly a function of phospholipid composition, but is likely coordinated by one or more specific binding proteins. [10]

A study by Li et al suggested that the Cys22-Cys27 disulfide bond in the protease domain of factor X modulates factor X’s clotting activity. Absence of the bond hinders insertion, following activation cleavage, of the catalytic domain’s N terminal, interfering with the zymogen-to-enzyme conformational transition. [11]

In addition to the procoagulant activity, factor X has mitogenic and pro-inflammatory activities. [2] It is reported to have mitogenic activity for smooth muscle cells and receptor-mediated proinflammatory activities. [2, 12]

Research indicates that factor X can be produced by malignant cells, with a study by Sierko et al reporting, for example, that it can be expressed by endometrial cancer cells; factor X showed medium expression in endometrial cancer cells but no expression in healthy endometrial cells. Moreover, protein Z and protein Z–dependent protease inhibitor, which work together to inhibit factor X, were strongly expressed in endometrial cancer cells, indicating involvement of these proteins in endometrial cancer. Investigations also suggest that gastric and colon cancer cells can express factor X. [13]

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