Direct measurement of the inhibition of thrombin by heparin cofactor II in the presence of the different ascidian DSs. A, inhibition of thrombin activity by HCII in the presence of DSs from H. pallida (- λ -), H. roretzi (- λ -), and C. intestinalis (- ν -). HCII (68 nM) was incubated with thrombin (15 nM) in the presence of various concentrations of glycans. After 60 seconds, the remaining thrombin or factor Xa activity was determined with a chromogenic substrate (ΔA405/min). The results are expressed as % of thrombin activity. B, IC50 (mg/ml) values for thrombin inhibition by HCII in the presence of DSs containing different percentages of 2,4-Disulfated disaccharide units (ΔDi2,4S) obtained from the ascidians H. pallida (- λ -), H. roretzi (- λ -), H. pyriformis (- ○ -), S. plicata (- ν -), Porcine intestinal mucosa (PIM) (- σ -), C. intestinalis (- ν -) and P. nigra (- □ -).