title: Factor VIIa/tissue factor-catalyzed activation of factors IX and X on a cell surface and in suspension: a kinetic study.
abstract: The kinetics of activation of factor IX and factor X by factor VIIa was studied in the presence of various sources of tissue factor: (1) a surface membrane of human ovarian carcinoma cell line, OC-2008 (2) the cell lysate (of OC-2008) and (3) reconstituted purified human tissue factor. The rates of activation of factors IX and X were monitored in activation peptide release assays using tritiated substrates. The results indicate that the apparent Km values for factor IX and factor X were similar for a given tissue factor, but varied with tissue factor source. The source of tissue factor greatly influenced the apparent differences in Vmax for factors IX and X. When a surface of monolayer provided tissue factor, the Vmax of factor IX was only 2-3 fold lower than factor X, but when either a cell lysate or purified tissue factor was the source of cofactor activity, the difference in Vmax rose to about 8-10 fold. Although, the tissue factor apoprotein in the cells was expressed entirely on the outer surface membrane, the activity of tissue factor on the intact cell surface was 50 to 100-fold lower than in the lysed cell preparation.
authors.affiliation: Department of Medicine, University of California, San Diego.
authors.forename: L V
authors.initials: LV
authors.lastname: Rao
authors.forename: T
authors.initials: T
authors.lastname: Robinson
authors.forename: A D
authors.initials: AD
authors.lastname: Hoang
mesh_terms: D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism; D004347:Drug Interactions; D015949:Factor IXa / Q000378:metabolism*; D015942:Factor VIIa / Q000494:pharmacology*; D015951:Factor Xa / Q000378:metabolism*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010051:Ovarian Neoplasms / Q000378:metabolism / Q000473:pathology; D013925:Thromboplastin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D013925:Thromboplastin; D015942:Factor VIIa; D015949:Factor IXa; D015951:Factor Xa