Thrombin

Definition

noun

An activated form of factor II that is generated in blood clotting and acts as a catalyst during the conversion of fibrinogen into fibrin


Supplement

Thrombin is a protease (34 kD) generated in blood clotting that acts on fibrinogen to produce fibrin. It consists of two chains: A and B chains that are linked by a disulphide bond. B chain has sequence homology with pancreatic serine proteases.

Thrombin is produced from prothrombin by the action either of the extrinsic system (tissue factor _ phospholipid) or, more importantly, the intrinsic system (contact of blood with a foreign surface or connective tissue). Both extrinsic and intrinsic systems activate plasma factor X to form factor Xa, which, then, in conjunction with phospholipid (tissue derived or platelet factor 3) and factor V, catalyses the conversion. In humans, it is encoded by the F2 gene.

Thrombin acts on soluble fibrinogen to be converted into insoluble fibrin strands. Thrombin time refers to the time required for the conversion of fibrinogen into fibrin.


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