Binding of basic pancreatic trypsin inhibitor and related isoinhibitors to leukocytic elastase. Determination of thermodynamic parameters.

The effect of temperature, ionic strength and solvation power of mono- and divalent cations on the interaction of BPTI-like inhibitors with human leukocytic elastase has been determined. The binding process is characterized by a non-linear dependence of the equilibrium association constant on 1/T indicating a thermal transition at temperature values ranging between 20 degrees C and 35 degrees C depending on the solvent. The marked dependence of the thermodynamic parameters (delta H degrees, delta S degrees, delta G degrees) and of the transition temperature on the concentration and nature of the cations present in solution seems to indicate that the transition, probably of conformational nature, is related to removal of water molecules upon enzyme/inhibitor complex formation.