[Structural aspects of the interaction between elastase and macromolecular inhibitors and of the regulation of its activity]

Conformational states of elastase complexed with macromolecular inhibitors were studied. Chemical reactivities of amino acid side-chains were used as conformational probes providing information on the structure of neighboring regions of the polypeptide chain. Variations in the chemical reactivity of ionizable groups of elastase and anhydroelastase complexed with alpha-1 antiprotease and ovomucoid were evidenced for segments 27-36, 42-53 and 118-136, which are not directly involved in interactions with the inhibitor. Studies of the denaturation of these complexes using differential chemical labeling showed that these conformational modifications were responsible for a decrease in overall stability of the enzyme complexed with the inhibitors. The magnitude of this decrease was estimated at 5 Kcal/mole. This finding suggests that interactions at the active site also induced changes in overall conformation of the molecule.