Fibrinogen is an abundant plasma protein (5-10uM) produced in the liver. The intact protein has a molecular weight of 340kD and is composed of 3 pairs of disulfide-bound polypeptide chains named Aalpha, Bbeta and gamma. Fibrinogen is a triglobular protein consisting of a central E domain and terminal D domains. Proteolysis by thrombin results in release of Fibrinopeptide A (FPA, Aa1-16) followed by Fibrinopeptide B (FPB, Bb1-14) and the fibrin monomers that result polymerize in a half-overlap fashion to form insoluble fibrin fibrils. The chains of fibrin are referred to as a, b and g, due to the removal of FPA and FPB. The polymerized fibrin is subsequently stabilized by the transglutaminase activated Factor XIII that forms amide linkages between g chains and, to a lesser extent, a chains of the fibrin molecules. Proteolysis of fibrinogen by plasmin initially liberates C-terminal residues from the Aa chain to produce fragment X (intact DE- D, which is still clottable). Fragment X is further degraded to nonclottable fragments Y (D-E) and D. Fragment Y can be digested into its constituent D and E fragments. Digestion of non-crosslinked fibrin with plasmin is very similar to the digestion of fibrinogen, which results in production of fragments D and E. Degradation of crosslinked fibrin by plasmin results in fragment DD (D-Dimer consisting of the D domains of 2 fibrin molecules crosslinked via the y chains), fragment E (central E domain) as well as DDE in which fragment E is non-covalently associated with DD. For human crosslinked fibrin, the relative weights of the cleavage fragments produced are: 184kD for fragment DD, 92kD for D, 50kD for E, 1.54kD for FPA and 1.57kD for FPB.
Intended for research use only. Not for use in human, therapeutic, or diagnostic applications.