Heparin and dextran sulfate concentration dependence of GDPC activation by thrombin. (A) Recombinant GDPC (0.75 μmol/L) was incubated with thrombin (5 nmol/L) in TBS buffer containing 2.5 mmol/L Ca²⁺, 1 mg/mL BSA, 0.1% PEG 8000, and indicated concentrations of heparin (○) or dextran sulfate (•) at room temperature for 10 minutes. After inactivation of thrombin activity by antithrombin, the initial rate of PC activation was measured by an amidolytic activity assay using SpPCa as described under the Materials and Methods. Less than 15% substrate was activated in all reactions. (B) The same as (A), except that TBS buffer contained 100 μmol/L EDTA, instead of Ca²⁺.