Activated thrombin (factor IIa) prothrombin -> activated thrombin (factor IIa) + thrombin activation peptide (prothrombinase catalyst) Authored: D'Eustachio, P, 2004-08-24 14:00:00 EC Number: 3.4.21 Pubmed14982929 Pubmed3052293 Reactome Database ID Release 43140664 Reactome, http://www.reactome.org ReactomeREACT_1446 The membrane-bound Va:Xa (prothrombinase) complex rapidly activates large amounts of thrombin.