Human Coagulation Factor XI
Domain Structure of Factor XI
The domain structure of the factor XI monomer is represented. The areas identified as R1 through R4 correspond to four tandem amino acid sequence repeats which ultimately comprise the heavy chain of factor XIa. During proteolytic activation by factor XIIa, the "CATALYTIC DOMAIN", which comprises the light chain of factor XIa, is cleaved from the heavy chain region. The heavy and light chains of factor XIa remain associated through a disulfide bond. The mature factor XI molecule is a homodimer composed of two apparently identical monomers which remain associated through disulfide bonds.
Price $82.00/50 µg ($76.00/min. 5)
Size 50 µg Formulation 50% glycerol/water (v/v) Storage -20°C Purity >95% by SDS-PAGE Activity Determination Clotting assay Shelf Life (properly stored) 12 months
|Gel||Novex 4-12% Bis-Tris|
|Load||Human Factor XI, 1 µg per lane|
|Standard||SeeBluePlus 2; Myosin (191 kDa), Phosphorylase B (97 kDa), BSA (64 kDa), Glutamic Dehydrogenase (51 kDa), Alcohol Dehydrogenase (39 kDa), Carbonic Anhydrase (28 kDa), Myoglobin Red (19 kDa), Lysozyme (14 kDa)|
|Special Notes||Heavy chain is a doublet due to the presence of up to 50% beta form. The conversion of alpha-Xa to beta-Xa occurs by autocleavage of alpha-Xa by alpha-Xa resulting in the loss of a COOH-terminal peptide.|
Factor XI is a plasma glycoprotein which circulates in a non-covalent complex with high molecular weight kininogen (1). The mature molecule is synthesized in the liver and is a two-chain homodimer with a molecular weight of approximately 160,000 (2,3). It is estimated that 5% of the total mass is attributable to carbohydrate (2). The two identical monomers have molecular weights of 80,000, and are joined together by disulfide bonds. Thus by SDS-PAGE analysis, factor XI appears as a single band both non-reduced (Mr=160,000), and reduced (Mr=80,000).
Factor XI circulates as a zymogen and requires proteolytic activation to acquire serine protease activity. The conversion of factor XI to factor XIa is catalyzed by factor XIIa, and results in cleavage of the Arg369-Ile370 bond in each monomer (3). Factor XIa consists of two NH2-terminal derived heavy chains, and two COOH-terminal derived light chains, all of which are held together by disulfide bonds. Factor XIa participates within the intrinsic pathway of coagulation by catalyzing the conversion of factor IX to factor IXa. A bleeding disorder called plasma thromboplastin antecedent deficiency results from a lack of factor XI procoagulant activity (4,5). The variable bleeding tendencies observed in factor XI deficient patients do not correlate with either factor XI activity or antigen levels. This latter observation may be related to the ability of the tissue factor/factor VIIa complex to also activate factor IX to IXa.
Historically, factor XI has been difficult to purify due to its relatively low concentration in plasma, and its susceptibility to proteolysis (6). Factor XI is purified from fresh frozen plasma that is stabilized by added inhibitors. The plasma is first treated with BaCl2 to remove the vitamin K-dependent proteins, and factor XI is then isolated by affinity chromatography. A final chromatography step on heparin sepharose yields a homogeneous preparation of intact factor XI. The finished product is supplied in 50% (vol/vol) glycerol/H2O and should be stored at -20oC.
|Localization||Plasma; in association with high molecular weight kininogen|
|Plasma concentration||2-7 µg/ml (2,3,7,8)|
|Mode of action||Zymogen; precursor to the serine protease factor XIa|
|Molecular weight||160,000 (human) (2,3)|
|Structure||homodimer consisting of two apparently identical subunits (Mr~80,000) held together by disulfide bonds. Monomers contain four tandem amino acid repeats that share homology with plasma prekallikrein (9).|
|Percent carbohydrate||5% (human) (2)|
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- Bouma, B.N. and Griffen, J.H., J. Biol. Chem., 252, 6432 (1977).
- Rosenthal, R.L., et al., Proc. Soc. Exp. Biol. Med., 82, 171 (1953).
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- Fujikawa, K., et al., Biochemistry, 25, 2417 (1986).
- Samuel, D., et al., Proc Natl Acad Sci U S A. 2007 October 2; 104(40): 15693–15698.(XI activation)
- Shariat-Madar, Z., et al., Blood. 2006 July 1; 108(1): 192–199. (use in PCR)
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