DETERMINATION OF ENZYME GLOBAL THERMOSTABILITY FROM EQUILIBRIUM AND KINETIC-ANALYSIS OF HEAT INACTIVATION

An equilibrium-kinetic description for the two-stage irreversible thermoinactivation of enzymes (N double left right arrow D double right arrow I) is examined by using chymotrypsin as a model. The parameter Delta G for enzyme unfolding (N double left right arrow D) and activation free energy for the D double right arrow I reaction (Delta G(i)(#)) were summed to provide an index of enzyme global thermostability (Delta G(#); Delta G(#) = Delta G + Delta G(i)(#)). There was good agreement between calculated and experimental global thermostability (i.e. enzyme stability with respect to reversible and irreversible thermoinactivation reaction steps) at 0-60 degrees C. The results indicate that enzyme global thermostability may be markedly dependent on the rate of enzyme folding.