Inhibition of TF-dependent factor Xa generation by factor VII.

The effect of zymogen factor VII on factor Xa generation by TF and the physiologic trace of factor VIIa was investigated by mixing a solution containing a limited amount of relipidated TF with a solution containing factor X and factor VIIa without (□) or with (▪) 10 nmol/L factor VII. Final concentrations in the reaction were as follows: 1.25 pmol/L TF, 100 pmol/L factor VIIa, and 500 nmol/L factor X. The initial inhibition and final identical rate of factor X activation in the reaction with factor VII is consistent with competitive binding to TF and feedback activation of the zymogen by factor Xa formed in the reaction.