Factor X Activated (Xa) from bovine plasma

Factor Xa is a serine endoproteinase and a member of the S1 peptidase family. Factor Xa plays a critical role in the coagulation cascade by catalyzing the proteolytic conversion of prothrombin to active thrombin. Factor Xa′s prothrombin conversion activity is greatly enhanced in vivo when complexed with factor V, calcium ions and phospholipids on the activated platelet surface.
The zymogen form, Factor X, is activated in vivo by two different pathways. The intrinsic pathway utilizes a catalytic complex composed of factor IXa, factor VIII, phospholipids and calcium ions. The extrinsic pathway utilizes a complex of factor VII and tissue factor. The factor X zymogen is a 55 KDa glycoprotein with a light and heavy chain joined by a single disulfide.

Bovine Factor Xa is used for site specific cleavage of recombinant fusion proteins containing an accessible Factor Xa recognition site for removal of affinity tags.

Fusion proteins are commonly expressed with a factor Xa cleavable Ile-Glu (or Asp)-Gly-Arg-↓-X sequence. Typically 1 mg of fusion protein can be incubated with 10 μg of factor Xa for 2.5 hours at 37 °C.

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.
pH Optimum: 7.6-8.0
Temperature Optimum: 37 °C

Lyophilized powder containing sodium citrate and sucrose

One unit of activated Factor X in the absence of Russell′s viper venom (RVV) gives the same substrate clotting time as one unit of plasma Factor × in the presence of RVV. Lipid is present in both systems.