American Society of Hirudotherapy

Binding of the recombinant proteinase inhibitor eglin c from leech Hirudo medicinalis to human leukocyte elastase, bovine alpha-chymotrypsin and subtilisin Carlsberg: thermodynamic study

Biochemistry article published in Journal of Enzyme Inhibition (1988)

Last Updated: June 18, 2026Reviewed by: ASH Editorial Board
Research article — evidence reviewArticle reference
Evidence: Research reportSalivary PharmacologyAscenzi P, Amiconi G, Menegatti E, Guarneri M, Bolognesi M, Schnebli HP · Journal of enzyme inhibition, 1988

Abstract

The effect of pH and temperature on the apparent association equilibrium constant (Ka) for the binding of the recombinant proteinase inhibitor eglin c from leech Hirudo medicinalis to human leukocyte elastase (EC 3.4.21.37), bovine alpha-chymotrypsin (EC 3.4.21.1) and subtilisin Carlsberg (EC 3.4.21.14) has been investigated. On lowering the pH from 9.5 to 4.5, values of Ka for eglin c binding to the serine proteinases considered decrease thus reflecting the acid-pK shift of the invariant histidyl catalytic residue (His57 in human leukocyte elastase and bovine alpha-chymotrypsin, and His64 in subtilisin Carlsberg) from congruent to 6.9, in the free enzymes, to congruent to 5.1, in the enzyme:inhibitor adducts. At pH 8.0, values of the apparent thermodynamic parameters for eglin c binding are: human leukocyte elastase - Ka = 1.0 x 10(10) M-1, delta G phi = -13.4 kcal/mol, delta H phi = +1.8 kcal/mol, and delta S phi = +52 entropy units; bovine alpha-chymotrypsin -Ka = 5.0 x 10(9) M-1, delta G phi = -13.0 kcal/mol, delta H phi = +2.0 kcal/mol, and delta S phi = +51 entropy units; and subtilisin Carlsberg - Ka = 6.6 x 10(9) M-1, delta G phi = -13.1 kcal/mol, delta H phi = +2.0 kcal/mol, and delta S phi = +51 entropy units (values of Ka, delta G phi and delta S phi were obtained at 21 degrees C; values of delta H phi were temperature independent over the range explored, i.e. between 10 degrees C and 40 degrees C; 1 kcal = 4184J).(ABSTRACT TRUNCATED AT 250 WORDS)

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't
Indexed MeSH termsAnimalsCattleChymotrypsinHumansKineticsPancreatic ElastaseProtease InhibitorsProtein BindingProteinsRecombinant ProteinsSerpinsSubtilisins

Summary

pH- and temperature-dependent thermodynamic analysis of leech eglin c binding to human leukocyte elastase, bovine alpha-chymotrypsin, and subtilisin Carlsberg reveals entropy-driven binding with comparable Ka ~5×10^9 M⁻¹ at pH 8.

Why This Matters for Hirudotherapy

This thermodynamic study investigated the binding of recombinant eglin c—derived from the leech Hirudo medicinalis—to human leukocyte elastase, bovine alpha-chymotrypsin, and subtilisin Carlsberg, examining the effects of pH and temperature on association equilibrium constants. Binding was characterized by very high affinity (Ka values on the order of 10^9–10^10 M^-1) and favorable entropy-driven thermodynamics, with the invariant catalytic histidyl residue showing an acid-pK shift upon inhibitor binding. For ASH, this work is relevant as it provides fundamental molecular-level characterization of a leech-secretome protease inhibitor's mechanism of action. The caveat is that this is a purely biophysical in vitro study with no clinical or whole-animal data, and it concerns a purified recombinant protein rather than hirudotherapy itself.

Citation

Binding of the recombinant proteinase inhibitor eglin c from leech Hirudo medicinalis to human leukocyte elastase, bovine alpha-chymotrypsin and subtilisin Carlsberg: thermodynamic study.

Ascenzi P, Amiconi G, Menegatti E, Guarneri M, Bolognesi M, Schnebli HP · Journal of enzyme inhibition, 1988

DOI

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