| 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. Additional Specifications: Localization: Plasma Mode of Action: Enzyme component of the Factor Xase complex Extinction Coefficient: E1%1cm, 280nm=14.0 (5) Structure: Two subunits, Mr=28,000 and 17,000 (5), NH2-terminal gla-domain, two EGF domains Post-translational Modifications: One b-hydroxyaspartate (3), twelve gla residues (4) Storage and Stability: May be stored at 4C for short-term only. Aliquot to avoid repeated freezing and thawing.. Store at -20C. Aliquots are stable for 6 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. |
