The self catalytic enzyme inactivation induced by solvent stirring: a new example of protein conformational change induction.

This article gives a new example of the protein conformational change induction. A well known example widely described in the literature is the prion, a protein whose the pathologic form, PrPsc, induces a conformational change of the normal form, PrPc, by interaction with it. This work highlights the existence of a self-catalytic conformation change for lysozyme. The functional modification of this protein is analysed in terms of irreversible loss of activity. Our experiments and the kinetic model derived from our results show that lysozyme inactivation is catalyzed by the inactivated lysozyme molecules; the lysozyme molecules with modified conformation induce a conformational change of native lysozyme molecules that in turn become inactive. This phenomenon is enhanced by stirring, which increases the probability and the efficiency of collisions between enzyme molecules. Furthermore, the self-catalytic inactivation kinetics of lysozyme is increased when salts are dissolved in the enzyme solution. Under these conditions, the protective effect due to the addition of salts, reported in previous literature, disappear. Salt-induced lysozyme destabilization effect can be observed. The salts enhance the aggregation of inactive enzyme molecules. A kinetic model of self catalytic inactivation of the enzyme has been developed, taking into account the results obtained with and without the addition of salts in aqueous solution.