Figure 4.

Effect of PZ and anti-ZPI antibodies on factor Xa inhibition in serum. Factor Xa (5 nM), CaCl₂ (4 mM), and cephalin (15 μM) with or without PZ (40 nM) were incubated 5 min at 22°C before the addition of barium-adsorbed serum (25%, vol/vol), which had been treated previously for 30 min with rabbit preimmune or immune anti-ZPI IgG (300 μg/ml). At the specified times thereafter, samples of the reaction mixtures were diluted in HSA with 1 mM EDTA and assayed for factor Xa activity by coagulation assay. (•), With PZ and preimmune IgG; (▾), with PZ and anti-ZPI IgG; (○), without PZ and with preimmune IgG; (▴), without PZ and with anti-ZPI IgG.