Enhancement of the TFPIα-mediated inhibition of thrombin generation by WT protein S and alanine composite variants. Thrombin generation was measured in protein S-depleted plasma supplemented with 50 µM phospholipids and 1 pM TF in the presence and absence of 1 nM TFPIα, and in the presence and absence of titrated (0-100 nM) WT protein S (A), protein S LG1A (B), LG1B (C), and LG1C (D). Representative experiments are shown (n = 3-4). (E-F) Normalized lag time (E) or peak thrombin (F) were plotted against protein S concentration. The lag time and peak height in the presence of TFPIα alone represent 100%. Results are expressed as mean ± SD (n = 3-4). PS, protein S.