Cofactor function of hTFAA. (A) Stimulation of amidolytic activity of 100 nmol/L human factor VIIa on the chromogenic substrate Spectrozyme FXa by wild-type sTF (▴) or hTFAA (▪). (B) Activation of FX by FVIIa in complex with mTF (⋅), sTF (▴, ▵) or hTFAA (▪, □). For measurements with mTF, the mTF concentration was 25 nmol/L and the FVIIa concentration was 5 nmol/L. Experiments with sTF and hTFAA used 250 nmol/L sTF or hTFAA and 50 nmol/L FVIIa (▵, □) or 500 nmol/L FVIIa and 2.5 μmol/L sTF or hTFAA (▴, ▪). The substrate (FX) concentration in these experiments was 1 μmol/L.