Thrombin inhibitor activated by the glycosaminoglycans, heparin or dermatan sulfate. In the presence of the latter, HC-II becomes the predominant thrombin inhibitor in place of antithrombin III (AT). The N-terminal acidic repeat region mediates, in part, the glycosaminoglycan-accelerated thrombin inhibition. N-glycosylated; different glycan composition appears to lead to two forms of this protein (56 and 60 kDa). Belongs to the serpin family.