Factor X EIA Set
Factor X (F.X, Stuart Factor) is a vitamin K-dependent glycoprotein
produced in the liver. The concentration of F.X in plasma is ~10
µg/ml (~170 nM). Factor X is expressed as a two-chain molecule
with a molecular weight of 59 kDa. The light chain (17 kDa) of F.X
contains a calcium-binding domain consisting of one hydroxyaspartic
acid and 11 gamma-carboxyglutamic acid (gla) residues. These
residues allow F.X to bind to membranes that contain acidic
phospholipids in a calcium dependent manner. This is followed by
two EGF-like domains. The heavy chain of F.X (42 kDa) consists of
the catalytic domain, carbohydrate and the activation peptide.
Activation of F.X to the active enzyme (F.Xa) results from cleavage at
residue Arg52 in the heavy chain of F.X by a complex of F.IXa,
cofactor VIIIa, calcium and negatively charged phospholipid surface
(the tenase complex), or by the F.VIIa-tissue factor complex. Both
activation pathways result in the release of the activation peptide
from the N-terminal of the heavy chain. The F.Xa generated is a
serine protease responsible for the activation of prothrombin to
thrombin in the presence of a phospholipid membrane, calcium and
cofactor Va. The activity of F.Xa in plasma is inhibited by
antithrombin (ATIII), α1antitrypsin, α2macroglobulin and tissue factor
pathway inhibitor (TFPI). The inhibitory activity of ATIII is stimulated
approximately 1000-fold by heparin.
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