Thermal inactivation of jack bean urease

Thermal inactivation of oligomeric enzymes results in complex structural changes. This work deals with thermal inactivation of a native hexamer, jack bean urease. In order to find the mechanism and kinetics of thermal inactivation corresponding well with the modification of tertiary and quaternary structure of this enzyme, several types of experiments were carried out in the temperature range of 65-85 °C. Inactivation data exhibited the characteristic biphasic character. Dynamic light scattering experiments revealed a significant increase of the mean hydrodynamic radius of urease with temperature and time. A significant contribution to understanding the mechanism of inactivation was provided by native gel electrophoresis data of inactivated samples. Simultaneous fit of inactivation data verified a two-step mechanism composed of reversible unfolding/folding reaction followed by a relatively fast aggregation of the denatured urease form. A complex reaction scheme containing numerous oligomeric forms was thus described by a relatively simple model which suitably represents the main types of reactions involved in the urease activity loss.