Thromb Haemost 1992; 67(06): 654-659
DOI: 10.1055/s-0038-1648518
Original Articles
Schattauer GmbH Stuttgart

Factor Vlla/Tissue Factor-Catalyzed Activation of Factors IX and X on a Cell Surface and in Suspension: A Kinetic Study

L Vijaya Mohan Rao
The Department of Medicine, University of California, San Diego, CA, USA
,
Thomas Robinson
The Department of Medicine, University of California, San Diego, CA, USA
,
An D Hoang
The Department of Medicine, University of California, San Diego, CA, USA
› Author Affiliations
Further Information

Publication History

Received 28 August 1991

Accepted after revision 20 January 1992

Publication Date:
03 July 2018 (online)

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Summary

The kinetics of activation of factor IX and factor X by factor Vila 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 002008) 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 K m 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 V max 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 V max 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 100fold lower than in the lysed cell preparation.