Fibrinogen & Fibrin

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• Physical Properties
• In vivo Processing
• Products

Physical Properties

Fibrinogen is synthesized in the liver and is circulated in plasma at ~200-450 mg/dL. It is a dimeric glycoprotein composed of three pairs of peptide chains. The two subunits are composed of a D domain which contains a globular region and an E domain which contains a disulfide bond that links the two subunits.

Molecular Mass:

Soluble Dimer: 340 kDa
α chain: 63.5 kDa
β chain: 56 kDa
γ chain: 47 kDa
E^1% = 15.1
PI ≈ 5.5

Fibrinogen is an acute phase protein that is part of the coagulation cascade of proteins. The end result of the cascade is the production of thrombin that converts fibrinogen to fibrin.

Thrombin rapidly proteolyzes fibrinogen, releasing fibrinopeptide A. The loss of this small peptide is not sufficient to make the resulting fibrin molecule insoluble, but it tends to form complexes with adjacent fibrin and fibrinogen molecules. Thrombin then cleaves a second peptide, fibrinopeptide B, from fibrin and the fibrin monomers formed then polymerize spontaneously to form an insoluble gel. The polymerized fibrin is held together by noncovalent and electrostatic forces and stabilized by the transamidating enzyme, factor XIIIa, that is produced by the action of thrombin on factor XIII. The insoluble fibrin aggregates (clots) and aggregated platelets then block the damaged blood vessel and prevent further bleeding. The amount of fibrinogen in the plasma can serve as a nonspecific indicator of whether or not an inflammatory process is present in the body. Fibrinogen from any mammalian source will be cleaved by thrombin from any mammalian source.¹

Hydrolysis of polymerized fibrin occurs when plasminogen is activated in the proximity of fibrin. Plasmin cleaves fibrin in the coiled region between the D and E domains as well as cleaving a peptide from the C-terminal region of the α-chain.

Products

References

The Plasma Proteins, 2nd ed., 2, Putnam, F. W., ed, p. 148.

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