Factor Xa catalyzes the hydrolysis of the Arg-Thr and then Arg-Ile bonds in prothrombin to yield active thrombin. The fairly strict recognition sequence is Ile-Glu (or Asp)-Gly-Arg-↓-X. It may sometimes cleave at other basic residues, depending on the conformation of the target protein. Factor Xa will not cleave if a proline residue follows the arginine of the recognition sequence.http://www.creative-enzymes.com/product/Native-Bovine-Factor-X-Activated-Xa-_1173.html