Although synthesized as a single polypeptide chain,<unk>  circulates as a homodimer. Every chain has a relative molecular mass of approximately 80000. Typical plasma concentrations of<unk>  are 5 μg/mL, corresponding to a plasma concentration (of<unk>  dimers) of approximately 30 nM. The<unk>  gene is 23kb in length, has 15 exons, and is found on chromosome 4q32-35.<unk>  consists of four apple domains, that create a disk-like platform around the base of a fifth, catalytic serine protease domain. One contains a binding site for thrombin, another for high molecular weight kininogen, a third one for<unk> X, heparin and glycoprotein Ib and the fourth is implicated in forming the<unk>  homodimer, including a cysteine residue that creates a disulfide bond. In the homodimer, the apple domains create two disk-like platforms connected together at an angle, with the catalytic domains sticking out at each side of the dimer. Activation by thrombin or<unk> Ia is achieved by cleavage of Arg369-Ile370 peptide bonds on both subunits of the dimer. This results in a partial detachment of the catalytic domain from the disk-like apple domains, still linked to the fourth domain with a disulfide bond, but now farther from the third domain. This is thought that this exposes the<unk> X binding site of the third apple domain, allowing<unk> 's protease activity on it.
Factor XI
Factor VIII
Factor VIII 
Factor IX
Thrombin
Prothrombinase
Von Willebrand factor
Fibrinogen