Properties of Glutamate Decarboxylase of Aspergillus oryzae and Its Application for Biotransformation of Glutamate into gamma-Aminobutyric Acid

The pellet of Aspergillus oryzae CICC 2026 was found to exhibit glutamate decarboxylase activity, and γ-aminobutyric acid was testified by paper chromatography. Its biochemical and kinetic properties were characterized. The results showed the pellet did not accumulate γ-aminobutyric acid (GABA) in the fermentation broth, but catalyzed the α-decarboxylation of MSG to GABA in the acetate buffer. The glutamate decarboxylase (GAD) of the pellet reached the maximum activity in submerged culture at 48 h. The optimum pH and temperature of the glutamate decarboxylase were 4.4 and 40 °C, respectively. The activity was stable between pH 4.4-4.8. It retained 80% of maximum activity after incubated at 30-40 °C for 2 h. Kinetic parameters Km and Vmax were found to be 17.86 mM and 1.49 µmol min-1 g-1, respectively. The influences of chemicals reagents on the catalytic activity were also evaluated that Fe3+ and Ca2+ decreased the enzyme activity by 96% and 25%; other reagents (K+, Mn2+ and Mg2+) did not significantly affect the enzyme activity. Conclusions can be drawn in this study that biotransformation of glutamate into γ-aminobutyric acid could be carried out by glutamate decarboxylase in the pellet of Aspergillus oryzae CICC 2026 at optimal conditions.