Purification and characterization of glutamate decarboxylase from Aspergillus oryzae

We purified glutamate decarboxylase (GAD) [EC4.1.1.15] from Aspergillus oryzae and characterized its biochemical and kinetic properties. GAD was purified by ammonium sulfate at 30-70% saturation and chromatographies on Sephacryl S-300, DEAE-FF and CM-FF. The purification of GAD from the crude enzyme solution was 40-fold and the recovery rate was 4.9%. About 230 mug of purified enzyme was obtained from 20 g of the mycelia of A. oryzae. The purified preparation of the enzyme showed a single protein band on SDS-PAGE. The molecular weight of purified GAD by SDS-PAGE and gel filtration was estimated to be 48 kDa and 300 kDa, respectively, suggesting that purified GAD had a hexameric structure. The K-m value for L-glutamic acid, a substrate of the enzyme, was estimated to be 13 mM. The optimum pH and temperature of GAD were 5.5 and 60degreesC, respectively. The GAD activity was stable up to 40degreesC.