Heparin cofactor II precursor fragment [Homo sapiens] is a peptide with the sequence H2N-Tyr-Glu-Ile-Thr-Thr-Ile-His-Asn-Leu-Phe-Arg-OH, MW=1406.58.

Heparin cofactor II(HCII) is a coagulation factor that inhibits IIa and is a cofactor for heparin and dermatan sulfate. The product encoded by this gene is a serine proteinase inhibitor which rapidly inhibits thrombin in the presence of dermatan sulfate or heparin. The gene contains five exons and four introns. This protein shares homology with antithrombin III and other members of the alpha 1-antitrypsin superfamily. Mutations in this gene are associated with heparin cofactor II deficiency. Heparin Cofactor II deficiency can lead to increased thrombin generation and a hypercoagulable state [1][2].