Title: Fibrin
CAS Registry Number: 9001-31-4
Literature References: Fibrin monomer is fibrinogen from which one or two peptides have been removed by means of thrombin: Laki, Chandrasekhar, Nature 197, 1267 (1963). The term fibrin is usually applied to polymerized fibrin monomer. Terminal clotting takes place in four steps: (1) fibrinogen hydrolyzes under the influence of thrombin into fibrin and fibrinopeptide fragments; (2) fibrin forms soft clots which can be readily dispersed; (3) thrombin activates fibrin-stabilizing factor, q.v., an enzyme precursor, present in blood plasma; (4) fibrin in the networks cross-links under the influence of the activated FSF to give the final hard clots: Chem. Eng. News 43, no. 32, 38 (1965); O. D. Ratnoff, B. Bennett, Science 179, 1291 (1973). Fibrin occurs in two principal forms, fibrin-i, "insoluble" fibrin, differing from fibrin-s, "soluble" fibrin, by urea solubility as well as other characteristics. Fibrin-i is formed through the reaction of a fibrinogen-like plasma protein, FSF, which in the presence of Ca2+ converts what would otherwise be a "soluble" weakly bonded gel into a covalently bonded, insol clot: Rosenberg, Carman, Nature 204, 994 (1964). Chemical studies of crosslinking segments: Chen, Doolittle, Proc. Natl. Acad. Sci. USA 66, 472 (1970); eidem, Biochemistry 10, 4486 (1971); Doolittle et al., Biochem. Biophys. Res. Commun. 44, 94 (1971). Reviews: W. H. Seegers, Prothrombin (Harvard University Press, 1962) 728 pp; Laki, Gladner, Physiol. Rev. 44, 127 (1964); Lorand, Fed. Proc. 24, no. 4, part 1, 784 (1965); A. L. Copley, Thromb. Res. 14, 249 (1979). Review of chemistry: several authors, Thromb. Diath. Haemorrh. Suppl. 39 (1970).
Fibroblast Growth Factor Fibrolase Fibronectins Fichtelite Ficin

Micrograph showing fibrin (dark pink amorphous material) in a blocked vein surrounded by extravasated red blood cells (right of image). An artery (left of image) and the amnion (far left of image) is also seen. Placenta in a case of fetal thrombotic vasculopathy. H&E stain.

Fibrin (also called Factor Ia) is a fibrous, non-globular protein involved in the clotting of blood. It is formed from fibrinogen by the protease thrombin, and is then polymerised to form a "mesh" that forms a hemostatic plug or clot (in conjunction with platelets) over a wound site.

Fibrin is involved in signal transduction, blood coagulation, and platelet activation.