Effect of the factor Xa and phospholipid concentration on the pSR. Normal pooled plasma was incubated for 30 minutes with and without antibodies against protein S. Coagulation was triggered with 5 mM CaCl₂ and either 6 μM phospholipid vesicles (DOPS/DOPC, 20/80, M/M) and 10, 20, 30, 40, 50, 70, and 90 pM factor Xa (A), or 20 pM factor Xa and 0.75, 1.5, 3, 6, 12, 24, and 48 μM phospholipid vesicles (DOPS/DOPC, 20/80, M/M) (B). The pSR is indicated as a function of factor Xa (A) or phospholipid concentration (B). Means ± SDs of 3 measurements are shown.