Thrombin is an enzyme that cleaves bonds after Arg and Lys, converts fibrinogen to fibrin and activates factors V, VII, VIII. Prothrombin is activated on the surface of a phospholipid membrane where factor Xa removes the activation peptide and cleaves the remaining part into light and heavy chains. This domain corresponds to the light chain of thrombin.

1: An overview of the structure and function of thrombin. Davie EW, Kulman JD; Semin Thromb Hemost. 2006;32:3-15. PMID:16673262