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Factor XIII or fibrin stabilizing factor is an enzyme () of the blood coagulation system that crosslinks fibrin. When thrombin has converted fibrinogen to fibrin, the latter forms a proteinaceous network in which every E-unit is crosslinked to only one D-unit. Factor XIII is activated by thrombin into factor XIIIa; its activation into Factor XIIIa requires calcium as a cofactor.
FXIII is known also as Laki-Lorand factor, after the scientists who first proposed its existence in 1948.Laki K, Lorand L. On the solubility of fibrin clots. Science 1948;108:280.
Genetics
Zymogene factor XIII is a 320000 Mr glycoprotein consisting of twice two subunits (2 A and 2 B), the genes for which are on different chromosomes:
- A subunit (6p25-p24). The transglutaminase part; this adds an alkyl group to the nitrogen on a glutamine residue, which binds in turn with a lysine on the other chain. The molecular weight of the A chain is approximately 83000.
- B subunit (1q31-q32.1). This has no clear enzymatic activity, and may serve as a carrier for the A subunit. The molecular weight of the B chain is approximately 76500.
Physiology
Typical concentrations of FXIII in plasma is 10 μg/ml (2A2B heterodimer), while the concentration of free B chain is 22 μg/ml. FXIII has a long half life, ranging from 5-9 days.
A clot that has not been stabilized by FXIIIa is soluble in 5 M urea, while a stabilized clot is resistant to this phenomenon.
Role in disease
Factor XIII deficiency may occur very rarely, and can cause a severe bleeding tendency. Incidence is 1 in a million to 1 in 5 million people. Most are due to mutations in the A subunit. Administration of recombinant A subunit improves clot stability and may become a therapeutic option for patients with this condition.
See also
Reference
External links
"Factor XIII"