Purification and characterization of a thermostable glutamate dehydrogenase from a thermophilic microorganism from Deception Island, Antarctica

摘要

Glutamate dehydrogenase(GDH) catalyzes the oxidative deamination of glutamate to α-ketoglutarate and ammonium ions. Currently the determination of ammonium and glutamate is carried out using a bovine GDH enzyme, which lacks optimal thermostability for long term storage at room temperature. From samples of Deception Island, Antarctica, we obtained the thermophilic bacteria PID 15 belonging to the Bacillus genera with high GDH specific activity. This new enzyme exhibited NAD+ dependent activity and no activity was observed when NADP+ was used. This enzyme shows a specific activity of 4.7 U?mg-1 for the oxidative deamination reaction and 15.4 U?mg-1 for the reduction of α-ketoglutarate. This enzyme has an optimum temperature of 65°C and p H of 8.5 for the oxidative deamination. For the reduction of α-ketoglutarate, the optimum temperature is 60°C, with a p H of 8.0. One of the most important characteristics of this enzyme is its ability to retain more than 60% of its activity when it is incubated for 8 h at 65°C. The enzyme is also able to retain full activity when it is incubated for 48 d at 4°C and over 80% of its activity when it is incubated at 25°C. Characterization of its kinetics suggests that it primarily catalyzes the formation of α-ketoglutarate. This enzyme has an important biological role in the catabolism of glutamate and may have some interesting biotechnological applications based on its thermostable properties.