These dimers and monomers are not known to participate in coagulation, whereas the tetramers do.A units have a mass of about 83 kDa, 731 amino acid residues, 5 protein domains (listed from the N-terminal to C-terminal, residue numbers are in brackets):
activation peptide (1–37)
β-sandwich (38–184)
catalytic domain (185–515), in which the residues C314, H373, D396 and W279 partake in catalysis
β-barrel 1 (516–628)
β-barrel 2 (629–731)B units are glycoproteins. Each has a mass of about 80 kDa (8.5% of the mass is from carbohydrates), 641 residues and 10 sushi domains. Each domain has about 60 residues and 2 internal disulfide bonds. Physiology
A subunits of human factor XIII are made primarily by platelets and other cells of bone marrow origin. B subunits are secreted into blood by hepatocytes. A and B units combine within blood to form heterotetramers of two A units and two B units. Blood plasma concentration of the heterotetramers is 14–48 mg/L and half-life is 9–14 days.A clot that has not been stabilized by FXIIIa is soluble in 5 mol/L urea, while a stabilized clot is resistant to this phenomenon. Factor XIII deficiency
Deficiency of Factor XIII (FXIIID), while generally rare, does occur, with Iran having the highest global incidence of the disorder with 473 cases. The city of Khash, located in Sistan and Balochistan provinces, has the highest incidence in Iran, with a high rate of consanguineous marriage. Diagnostic use
Factor XIII levels are not measured routinely, but may be considered in patients with an unexplained bleeding tendency.
They are responsible for differentiating into a diverse group of cells that reach different areas of the body. The neural tube and neural crest are derived from the ectoderm; the neural tube goes on to form the brain and spinal cord, while the neural crest cells eventually go on to form various bones and cartilage of the skull and face by migrating through the pharyngeal arches. They also differentiate into the stria vascularis of the cochlea, the nerves and glia of the intestines (myenteric plexus), Schwann cells, which myelinate the peripheral nervous system to allow sufficient conductivity, odontoblasts, which produce dentin deep in the teeth, some neuroendocrine cells, connective tissue around the salivary, lacrimal, pituitary, thymus and thyroid glands, connective tissue of the eye, such as the stroma of the iris and cornea and the trabecular meshwork, and melanocytes, including those in the stroma of the iris that give rise to brown eye colour through melanin. Neural crest cells also have a role in muscle formation, including the wall muscle of certain cardiac arteries. Causes of subtypes
Type 1 is caused by an autosomal dominant mutation in the gene PAX3. PAX3, or paired box 3, is a transcription factor that has a role in maintaining an open window of time for certain neural crest cells (such as those of the head and eyes) to divide and migrate before their terminal differentiation (i.e. to maintain them in the stem-cell state).