Double-headed protease inhibitors from black-eyed peas. V. Analysis of the energetics of protease-inhibitor interactions.

The half-site reactivity of trypsin and chymotrypsin binding to two double-headed black-eyed pea protease inhibitors a trypsin-chymotrypsin inhibitor (BEPCI) had a trypsin inhibitor (BEPTI), is explained in terms of the energetics of these inhibitor-protease interactions. Free energy diagrams are constructed to facilitate interpretation of the energetics. Coupling-free energies are calculated to reflect the magnitude of the interdependence of protease-binding (alloassociation) and inhibitor subunit interactions (isoassociation). The experiment observation of the predominance of liganded monomer complexes for the lima bean inhibitor and the Bowman-Birk soybean inhibitor and the predominance of half-site-liganded complexes for BEPCI and BEPTI is the direct result of the magnitudes and signs of the coupling free energies which result from these protease-inhibitor interactions.