American Society of Hirudotherapy

A new factor Xa inhibitor (lefaxin) from the Haementeria depressa leech

Biochemistry study published in Thrombosis and Haemostasis (1999)

Last Updated: June 18, 2026Reviewed by: ASH Editorial Board
Research article — evidence reviewArticle reference
Evidence: Observational studyGenomics & ProteomicsSalivary PharmacologyFaria F et al. · Thrombosis and haemostasis, 1999

Abstract

The salivary complex of the leech Haementeria depressa produces potent anticoagulant components. Among them, a protein named lefaxin inhibits factor Xa (FXa). Lefaxin was purified to homogeneity from dissected salivary complexes by gel filtration in Sephadex G-150 followed by two ion exchange chromatography steps in Mono-Q. Inhibition of FXa by lefaxin was demonstrated by the inhibition of its amidolytic activity, measured with chromogenic substrate S-2765 (apparent K(I) of 4 nM), and of its ability to inhibit thrombin generation in the prothrombinase complex (EC50 of 40 nM). Lefaxin has a molecular weight of 30 kDa and an isoelectric point of 5.7. It is made of a polypeptide chain whose N-terminal sequence shows no similarity with that of other FXa inhibitors (antistasin and ghilianten) isolated from leech saliva. On the other hand, the N-terminal sequence of lefaxin presents significant sequence similarity with nitric oxide carrier proteins myohemerythrin from the annelid Nereis diversicolor and prolixin S from the triatoma Rhodnius prolixus. Interestingly, prolixin S also proved to be an anticoagulant protein acting on FXa.

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

Publication typeComparative StudyJournal ArticleResearch Support, Non-U.S. Gov't
Indexed MeSH termsAmino Acid SequenceAnimalsAnticoagulantsBlood CoagulationChromatography, GelChromatography, Ion ExchangeChromogenic CompoundsFactor Xa InhibitorsHelminth ProteinsHemeproteinsHemerythrinHumans

Summary

Isolates lefaxin, a 30-kDa Factor Xa inhibitor from Haementeria depressa — characterizes inhibition kinetics and anticoagulant activity.

Why This Matters for Hirudotherapy

This study purified lefaxin, a factor Xa inhibitor, from the salivary complex of the leech Haementeria depressa, demonstrating inhibition of FXa amidolytic activity (apparent Ki ~4 nM) and of thrombin generation in the prothrombinase complex (EC50 ~40 nM). Lefaxin is a 30-kDa protein (pI 5.7) whose N-terminal sequence shows no similarity to other leech FXa inhibitors antistasin and ghilianten, but does share similarity with myohemerythrin from the annelid Nereis diversicolor and prolixin S from the triatoma Rhodnius prolixus, itself an FXa-targeting anticoagulant. This is relevant to ASH as it expands the known diversity of leech-secreted FXa inhibitors. However, the study is limited to in-vitro biochemical purification and characterization; no in-vivo or clinical data are reported.

Citation

A new factor Xa inhibitor (lefaxin) from the Haementeria depressa leech.

Faria F et al. · Thrombosis and haemostasis, 1999

DOIPubMed

Added to ASH library: May 27, 2026 · Site last updated: June 18, 2026

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