Fibrinopeptide A (FPA)

Fibrinopeptide A is a substance released as part of the blood clotting process. Fibrinogen, the principal protein of vertebrate blood clotting is a hexamer containing two sets of three different chains (alpha，beta, and gamma), linked to each other by disulfide bonds. The N-terminal sections of these three chains contain the cysteines that participate in the cross-linking of the chains.

The C-terminal parts of the alpha, beta and gamma chains contain a domain of about 225 amino-acid residues, which can function as a molecular recognition unit. In fibrinogen as well as in angiopoietin this domain is implicated in protein-protein interactions. In lectins, such as mammalian ficolins and invertebrate tachylectin 5A, the fibrinogen C-terminal domain binds carbohydrates. On the fibrinogen alpha and beta chains, there is a small peptide sequence (called a fibrinopeptide). It is these small peptides that prevent fibrinogen spontaneously forming polymers with itself.