Binding of the bovine basic pancreatic trypsin inhibitor (Kunitz) to human Lys77-plasmin

Enea Menegatti, Mario Guarneri, Martino Bolognesi, Paolo Ascenzi, Gino Amiconi

Research output: Contribution to journalArticlepeer-review


The effect of pH and temperature on the association equilibrium constant (Ka) for the binding of the bovine basic pancreatic trypsin inhibitor (BPTI, Kunitz inhibitor) to human Lys77-plasmin has been investigated. Ka values decrease with decreasing pH, reflecting the acid-pK and -midpoint shifts, upon BPTI binding, of a single ionizable group, between pH 5 and 9, and of a three-proton transition, between pH 3 and 5. At pH 8.0, values of thermodynamic parameters for BPTI binding to human Lys77-plasmin are: Ka = 1.2×109m-1, ΔG ° = - 12.2 kcal/mol, and ΔS ° = + 49 entropy units (at 21 °C); and ΔH ° = + 2.3 kcal/mol (temperature independent between 5 °C and 45 °C; l kcal = 4184 J). BPTI binding properties of human Lys77-plasmin have been analysed in parallel with those of serine (pro)enzymes acting on cationic and non-cationic substrates. Considering the known molecular structures of homologous serine (pro)enzymes, or Kunitz and Kazal-type inhibitors and of their complexes, the observed binding behaviour of BPTI to human Lys77-plasmin was related to the inferred stereochemistry of the enzyme-inhibitor contact region.

Original languageEnglish
Pages (from-to)295-297
Number of pages3
JournalJournal of Molecular Biology
Issue number2
Publication statusPublished - Sep 20 1986

ASJC Scopus subject areas

  • Virology


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