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). Also inhibits chymotrypsin, but in a glycosaminoglycan-independent manner. Expressed predominantly in liver. 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 (68 and 72 kDa). Belongs to the serpin family.