Initial rate of PC activation by fXa on phospholipids in the presence and absence of the polysaccharides. (A) PC (0.75 μmol/L) was incubated with 5 nmol/L fXa on 100 μg/mL PC/PS (•, ○) or PC/PS/PE (▪, □) phospholipid vesicles in the absence (•, ▪) or the presence (○, □) of 25 μg/mL heparin in TBS buffer containing 5 mmol/L Ca²⁺, 1 mg/mL BSA, and 0.1% PEG 8000. At indicated time intervals, the rate of PC activation was measured by an amidolytic activity assay as described under the Materials and Methods. (B) The same as (A), except that 25 μg/mL dextran sulfate instead of heparin was used in the reactions.