| Activation of Factor X By Factor IXa: The intrinsic factor Xase complex consists of an enzyme, factor IXa, and a cofactor, factor VIIIa, assembled on a phospholipid surface in the presence of calcium ions. The enzyme complex proteolytically cleaves a 10,000 molecular weight activation peptide from the NH2-terminal of the heavy chain of factor X, thus expressing the active-site of factor Xa. Factor IXa is produced from its inactive precursor, factor IX, via proteolytic cleavage by factor XIa or the tissue factor/factor VIIa/phospholipid complex. The activation results from the cleavage of two peptide bonds in the factor IX molecule, releasing an activation glycopeptide with an apparent molecular weight of 10,000. The heavy chain of factor IXa (Mr=28,000) contains the serine protease catalytic domain, while the light chain (Mr=17,000) contains the membrane binding domain. Factor IXa functions as a serine protease involved in the activation of the zymogen, factor X, to form the enzyme, factor Xa. The factor IXa enzymatic activity is greatly enhanced by inclusion of its cofactor, factor VIIIa, in the presence of calcium ions on a phospholipid surface. Factor IXa is readily inhibited by antithrombin III, and this inhibition is greatly accelerated by the presence of heparin. Factor IXa is not inhibited by DFP. Specific Activity (Determined by Factor IX Clotting Assay): As reported Unit Definition: 1u is equivalent to the Factor IX activity in 1ml if normal plasma. Extinction Coefficient: E1%1cm, 280nm=14.0 (5) Mode of Action: Enzyme component of the Factor Xase complex Structure: Two subunits, Mr 28kD and 17kD (5), NH2-terminal gla-domain, two EGF domains Post-translational modifications: One b-hydroxyaspartate , twelve gla residues Storage and Stability: For long-term storage, store at -20C. Aliquots are stable for12 months after receipt at -20C. 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. Related Products: F0017-21: Factor IXa with the active site irreversibly blocked by the fluorescent inhibitor, Dansyl-EGRck . F0017-22: Factor IXa with the active site irreversibly blocked by the tripeptide chloromethyl ketone, EGRck. |
