MODELING OF INACTIVATION PHENOMENA IN OLIGOMERIC ENZYMES

Theory of oligomeric proteins characterises their structure as a dynam ic equilibrium between the oligomeric protein and its subunits. In ord er to investigate this hypothesis, the kinetics of thermal inactivatio n of purified yeast invertase (E.C.3.1.2.26) was measured within a tem perature interval of 40 - 60 degrees C. As this enzyme is supposed to be a homodimer, a model was suggested comprising a dynamic equilibrium between a dimer, D, and a monomer M, which further denaturates to an inactivated form I. The experiments were carried out at various temper atures. All data were fitted simultaneously using the Arrhenius equati on for the characterisation of temperature dependence of rate constant s. The differential equations describing the system (non-linear with r espect to parameters as well as variables) were solved using a Runge-K utta method. The results showed that a dimer-monomer equilibrium exist ed prior to starting inactivation. The activation energies of both rea ctions as well as the reaction enthalpy of dimer dissociation were det ermined. This study showed that the modelling of inactivation kinetics is a useful tool in understanding both denaturation phenomena and pro tein structure.