Kinetics of thermal deactivation of enzymes: a simple three parameters phenomenological model can describe the decay of enzyme activity, irrespectively of the mechanism.

Heat induced enzyme inactivation or protein denaturation is now well docume nted, due to progresses in methods, instruments and computation resources. Complex mechanisms, rather than the classic simple "one step - two states" model (still in use) are recognized in many cases, leading investigators to manipulate more or less complicated kinetic expressions describing the hea t induced decay of enzyme activity. We show that the different kinetic expressions related to different mechani sms among the most frequently encountered can be arranged in a common simpl e three-parameters biexponential equation. This unifying simplification is of interest for people focusing attention t o phenomenological rather than mechanistic description of the kinetics of h eat induced enzyme deactivation. Moreover, the reduction in the number of p arameters reduces the risk of cross-correlation and allows a better estimat ion of the apparent rate constants (which are in many cases the pertinent r equired information). It also illustrates the difficulty to make inference of mechanism from kinetics, since the same equation applies for a variety o f mechanisms ("kinetic homeomorphism") - in particular, it stresses out the need of caution when reporting on existence of isoenzymes from deactivatio n kinetics. Application of this simple 3-parameters biexponential kinetic expression ha s been validated with a number of results in the Literature and current inv estigations in our laboratory. Two examples are given. (C) 2000 Elsevier Sc ience Inc. All rights reserved.