Activation of the zymogen, factor X, by either the intrinsic or extrinsic factor Xase complexes produces the active serine protease factor Xa (1,2). The activation of factor X requires proteolytic cleavage of the heavy chain, resulting in the release of an activation glycopeptide. The heavy chain region in factor Xa contains the serine protease catalytic domain, while the light chain, as in the zymogen, contains the membrane binding domain.
Factor Xa participates in the prothrombinase complex, which catalyzes the rapid conversion of prothrombin to thrombin. Prothrombinase is an enzyme complex composed of factor Xa (enzyme) and factor Va (cofactor) assembled on a cellular surface in the presence of calcium ions. Although factor Xa can independently catalyze the activation of prothrombin, the rate at which this reaction occurs is increased nearly 300,000-fold with complete assembly of the prothrombinase complex. The clotting activity of factor Xa in vivo is terminated by either inactivation of the cofactor, factor Va, or by direct inhibition of factor Xa by inhibitors, such as ATIII, after disassembly of the prothrombinase complex.
In recent years, molecular biologists have utilized factor Xa for site specific cleavage of fusion proteins expressed in bacteria (9-12). A factor Xa-sensitive site is incorporated between the recombinant protein of interest and peptides or proteins which facilitate purification and/or expression. The target protein is released from the expressed hybrid by cleavage with factor Xa. The factor Xa can then be easily removed by affinity chromatography.
In addition to its broad application in coagulation research factor Xa can be used for site specific cleavage of fusion proteins. A factor Xa sensitive site is incorporated between the recombinant protein of interest and peptides or proteins which facilitate purification and/or expression. The target protein is released from the expressed hybrid by cleavage with factor Xa. Factor Xa can then be easily removed by affinity chromatography.
Localization: Plasma
Mode of Action: Enzyme component of the prothrombinase complex
Extinction Coefficient:E1%1cm, 280nm= 11.6 (6)
Specific Activity: ~1000u/mg
Structure: Two subunits, Mr=16,200 and 29,000 (6), NH2-terminal gla domain, two EGF domains
Percent Carbohydrate: 3.0% (8)
Post-translational Modifications: Eleven gla residues, one beta-hydroxyaspartate
Storage and Stability:May be stored at 4°C for short-term only. Aliquot to avoid repeated freezing and thawing. Store at -20°C. Aliquots are stable for at least 6 months at -20°C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer.
