A novel thermostable glucose dehydrogenase varying temperature properties by altering its quaternary structures

Abstract

A novel thermostable glucose dehydrogenase was purified from a Gram-negative moderate thermophilic bacterium isolated from soil near a hot spring. The homogeneously purified enzyme sample showed two peaks at the optimum temperature for reaction, i.e., at around 45 and 70°C. However after 30 min of incubation at 70°C, the enzyme showed only one peak at 75°C. From the results of native and SDS-PAGE of this enzyme, it was suggested that at temperatures below 45°C, this enzyme was a hetero-oligomeric complex constructed from two distinct peptides with MWs of 67,000 and 43,000, thereby showing that the optimum temperature for reaction was 45°C. Incubation at 70°C of this hetero-oligomer dissociated each subunit and resulted in a single peptide enzyme with a MW of 67,000 that showed GDH activity with optimal temperature only at 75°C. This single peptide enzyme retained more than 80% of its initial activity even after 30 min of incubation at 60°C. Therefore, we concluded that this novel enzyme showed a different optimum temperature for reaction according to its quaternary structure.