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 documented, 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 heat induced decay of enzyme activity. We show that the different kinetic expressions related to different mechanisms among the most frequently encountered can be arranged in a common simple three-parameters biexponential equation. This unifying simplification is of interest for people focusing attention to phenomenological rather than mechanistic description of the kinetics of heat induced enzyme deactivation. Moreover, the reduction in the number of parameters reduces the risk of cross-correlation and allows a better estimation of the apparent rate constants (which are in many cases the pertinent required information). It also illustrates the difficulty to make inference of mechanism from kinetics, since the same equation applies for a variety of mechanisms ("kinetic homeomorphism") - in particular, it stresses out the need of caution when reporting on existence of isoenzymes from deactivation kinetics. Application of this simple 3-parameters biexponential kinetic expression has been validated with a number of results in the Literature and current investigations in our laboratory. Two examples are given. (C) 2000 Elsevier Science Inc. All rights reserved.