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 g 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 60˚C, respectively. The GAD activity was stable up to 40˚C.Keywords: glutamate decarboxylase, Aspergillus oryzae, purification, ␥-amino-butyric acid Glutamate decarboxylase (GAD; EC4.1.1.15) produces ␥-amino-butyric acid (GABA) from glutamate. GABA has several physiological effects on the human body, including neurotransmitting, hypotensive and diuretic effects. Several attempts to enrich GABA in functional foods have been reported: GABArich green tea produced by anaerobic treatment of green tea (Ohmori et al., 1987), GABA accumulation in red mold rice (Tsuji et al., 1992), GABA accumulation in rice germ by soaking in water (Saikusa et al., 1994), GABA enrichment in brown rice by high-pressure treatment (Kinefuchi et al., 1999) and GABA production by lactic acid bacteria .We have recently found high GAD activity in Aspergillus oryzae cultured in a liquid medium, and it was specially rich in A. oryzae used for miso and sake brewing (Tsuchiya & Nishimura, 2002a). Furthermore, we also reported that the batch reactor using pellet form mycelium of A. oryzae (for miso production), which was cultured in liquid medium achieved an extremely high GABA production rate (8.5 mmol GABA/g Aspergillus mycelium/h) (Tsuchiya et al., 2002b).GAD is widely distributed in animate nature. In mammals, GAD has been purified from human brain (Blindermann et al., 1978) and mouse brain (Wu et al., 1973). In higher plants, GAD has been purified from squash (Matsumoto et al., 1986). In bacteria, the enzymatic properties of GAD have been reported in both Escherichia coli (Shikuya & Schwert, 1960;Fonda, 1985) and Lactobacillus brevis . Although GAD obtained from A. oryzae has not been purified, the gene was recently cloned and the nucleotide sequence was determined (Iwai et al., 2001). The detailed biochemical nature of the enzyme is unclear, which we believe important in promoting the GABA production in food processing by effective utilization of the GAD from A. oryzae. In this study, we purified GAD from the mycelium of A. oryzae and examined some biochemical characteristics of the enzyme. Materials and MethodsMicroorganism and the culture conditions Aspergillus oryzae used in this study was isolated from tane-koji SR-108...

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Inoculation of Zygosaccharomyces rouxii into a soy sauce mash free from lactic acid bacteria at 106 cells mL−1 resulted in the formation of the flavour‐active compound HEMF over a number of days at 30°C. Delays in inoculation up to 14 days after production of the mash greatly increased the amount of HEMF formed and under some conditions concentrations in the commercial range were achieved without addition of any other microorganisms.

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