American Society of Hirudotherapy

Thrombin inhibition by hirudin: how hirudin inhibits thrombin

Research article published in Haemostasis (1991)

Last Updated: June 18, 2026Reviewed by: ASH Editorial Board
Research article — evidence reviewArticle reference
Evidence: Narrative reviewDrug DevelopmentFenton J et al. · Haemostasis, 1991

Abstract

In addition to its classical active-site regions (catalytic site and adjacent regions), alpha-thrombin has a unique anion-binding exosite, which is functionally independent of the catalytic site and is involved in fibrin(ogen) recognition. This exosite also accounts for adhesion to negatively charged surfaces (e.g., glass), binding to cell surfaces, and interactions with the anionic tail of hirudin. Hirudin (as an apolar, tridisulfide-linked core structure followed by its anionic tail) interacts with alpha-thrombin by apolar (e.g., catalytic-site and adjacent regions of thrombin), as well as by ionic binding (e.g., anion-binding exosite). Circular dichroism measurements reveal a sigmoidal nonadditivity for the hirudin tail fragments, which block fibrinogen-clotting activity without interfering with tripeptide chromogenic substrate activities. Such fragments, however, inhibit factor V activation to much lesser extents than hirudin, where factor V activation is the key step in regulating thrombin generation by hirudin or heparin/antithrombin III. Hirudin-derived antithrombotics may thus have differential modes of action in hemostasis and wound healing processes.

Abstract sourced from PubMed (NCBI) for the cited record. See the original publication for the authoritative version.

Publication typeJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, P.H.S.Review
Indexed MeSH termsAmino Acid SequenceAnimalsAnionsBinding SitesCircular DichroismEnzyme ActivationFactor VFibrinogenHirudinsMolecular Sequence DataMolecular StructurePeptide Fragments

Summary

In addition to its classical active-site regions (catalytic site and adjacent regions), alpha-thrombin has a unique anion-binding exosite, which is functionally independent of the catalytic site and is involved in fibrin(ogen) recognition.

Why This Matters for Hirudotherapy

This study examined the molecular mechanism by which hirudin inhibits alpha-thrombin, characterizing how hirudin's apolar, tridisulfide-linked core and anionic tail engage both thrombin's catalytic site and its functionally independent anion-binding exosite. Circular dichroism experiments revealed that hirudin tail fragments block fibrinogen-clotting activity without affecting tripeptide chromogenic substrate hydrolysis, yet inhibit factor V activation less potently than intact hirudin—a step identified as key in regulating thrombin generation. These findings are mechanistically relevant to understanding hirudin as a direct thrombin inhibitor, since the abstract itself concludes that hirudin-derived antithrombotics may have differential modes of action in hemostasis and wound healing. However, the abstract makes no mention of leeches, salivary secretions, or leech therapy, so the connection to hirudotherapy is indirect, limited to the molecular pharmacology of the thrombin–hirudin interaction rather than any clinical or organism-level context.

Citation

Thrombin inhibition by hirudin: how hirudin inhibits thrombin.

Fenton J et al. · Haemostasis, 1991

DOI

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