[Interpretation of thermograms of protein denaturation in non-equilibrium conditions]

Data are presented concerning the effect of heating rate on the denaturation parameters of small and oligomeric globular proteins: Kunitz trypsin inhibitor from soybeans and 1,5-Ribulose Bisphosphate Carboxylase from tobacco leaves. Substantional dependence of denaturation temperature on the heating rate reflects non-equilibrium pattern of denaturation of these proteins under experimental conditions. To interpret these data a kinetic approach is proposed, which permits determination of equilibrium value of the denaturation temperature and of the constant of de- and renaturation rate. The conformation transitions in the proteins studied are shown to be relatively slow processes. Their rate is comparable to the velocity of temperature change in a calorimeter, which is the cause of non-equilibrium effects in a calorimetric experiment.