Factor X

Literature References: Enzyme which is activated by a complex of factors IX, VIII, calcium ions and phospholipid, or by factor VII and tissue factor in the intrinsic and extrinsic pathways of blood coagulation resp. Non-physiological activators are trypsin and a specific protein from Russel's viper venom: see Fujikawa et al., Biochemistry 11, 4892 (1972). Active factor X apparently acts upon factor V, q.v. in the presence of calcium ions and lipid to form a complex which activates the conversion of prothrombin to thrombin. Present in both plasma and serum because neither increases nor decreases during clotting. Presumably synthesized in the liver because level is reduced with coumarin drugs and in liver disease. Isoln and characterization of bovine factor X: eidem., ibid. 4882. Factor Xa is a serine protease which, in the presence of factor V, Ca2+ ions and phospholipids, activates prothrombin. Severe deficiency causes hemorrhagic state resembling hemophilia. Mild deficiency may result in easy bruising. In severe cases deep muscular and joint hemorrhages occur. Improved purification and bibliography of earlier isoln procedures: Bajaj, Mann, J. Biol. Chem. 248, 7729 (1973). Comparison of the molecular forms generated by the different methods of activation: Radcliffe, Barton, ibid. 6788. Review: Graham, Hougie in Thombolytic Activity and Related Phenomena, I. S. Wright et al., Eds. (Schattauer-Verlag, Stuttgart, 1961) pp 416-420; C. M. Jackson, Thromb. Diath. Haemorrh. Suppl. 57, 197-216 (1974). Reviews on prepn, physical properties and function in the coagulation process: K. Fujikawa, E. W. Davie, Methods Enzymol. 45B, 89 (1976); J. Jesty, Y. Nemerson, ibid. p 95.

Properties: Stable at room temperature for several days. Adsorbed by BaSO4, Al(OH)3, Ca3(PO4)2, Seitz filters, bentonite and DEAE cellulose. At 56° is destroyed rapidly, in serum, less rapidly as citrate eluate. At 65° is destroyed rapidly in any form. Stable between pH 6.1-9.0. Soluble in water. Precipitates from water between pH 8-4. Isoelec pt pH 4.3.