Activation of human factor X by the complex formed between 10 nmol/L FVIIa and 1 nmol/L wild-type sTF (▴) or hTFAA (▪) in the presence of phospholipid vesicles (0.5 mmol/L phospholipid) prepared from a 70/30 mixture of PC/PS. Initial rates of FXa formation were determined and are plotted versus substrate (FX) concentration. The solid lines are the result of nonlinear regression analysis by using the Michaelis-Menten equation.