Fibrinmonomere

Fibrinmonomere, also known as the fibrin monomer, is the soluble product formed when thrombin cleaves fibrinogen during the blood coagulation cascade. Thrombin removes fibrinopeptides A and B from the Aα and Bβ chains, exposing N-terminal knobs that can interact with complementary holes on adjacent molecules. This conversion creates a competent but unassembled unit capable of assembling into a polymer.

Polymerization occurs as exposed knobs bind to corresponding holes on neighboring fibrin monomers, driving end-to-end assembly into double-stranded protofibrils. These protofibrils associate laterally to form a three-dimensional fibrin network. The process is calcium-dependent and proceeds under the influence of the thrombin–fibrin architecture that defines clot structure. The resulting fibrin network serves as the scaffold of the hemostatic clot.

Stabilization of the network is achieved through covalent crosslinking by activated Factor XIII (XIIIa). XIIIa forms ε-(γ-glutamyl)lysine crosslinks that first stabilize the gamma chains and subsequently the alpha chains, increasing mechanical strength and resistance to proteolysis. This crosslinking converts a soluble polymer into a highly resistant insoluble clot.

Clinical and laboratory relevance of fibrinmonomere lies in its central role in hemostasis. Abnormal fibrin monomer formation or polymerization can affect clot structure and stability, contributing to bleeding or thrombotic disorders. In laboratory settings, assays that reflect thrombin generation or fibrin polymerization can provide information about coagulation status and fibrin network formation.