Fibrinogen, the precursor of fibrin, is the coagulable protein in the blood plasma of vertebrates. Fibrinogen consists as a dimer of 3 pairs of non-identical chains a (Mr= 66,800), b (Mr= 52,000) and g (Mr=46,500) cross-linked by disulfide bonds in their N-terminal segments. The molecule has 2 terminal D domains and one central E domain, all three domains are separated when fibrinogen is degradated by plasmin. MW is 340 kDa. Concentration in human plasma is 2-3 mg/ml.