Denaturation of thermophilic and mesophilic 6-phosphogluconate dehydrogenase by 8M urea

The denaturation reaction of 6-phosphogluconate dehydrogenase (6-phospho-D-gluconate: NADP oxidoreductase (decarboxylating EC 1.1.1.44) from B. Stearothermophilus and E. coli in 8 M urea has been compared. The rates of denaturation were evaluated from the fluorescence quenching that occurs at 334 nm. The thermophilic enzyme has been found about ten times more resistant to the action of the denaturating agent, and showed a biphasic denaturation process, whereas the E. coli enzyme followed a single first-order kinetics.