[Object] Gamma-Amino Butyric Acid (GABA), a four-carbon non protein amino acid, is widely distributed in nature and acts as the major suppressive neurotransmitter in the mammalian central nervous system. Recently, GABA has been reported to have several physiological functions such as antihypertensive, diuretic, relaxing and antidiabetic effects. Due to these unique biological functions, GABA has been used as functional ingredients for functional foods. Glutamic Acid Decarboxylase (GAD), which catalyzes decarboxylation of L-glutamic acid to GABA, has been purified from mammals, higher plants, and some microorganisms and their properties have already been reported. On the other hand, mushrooms are commonly appreciated as healthy food due to their nutritional properties, such as low calorie, rich in fiber, vitamin and mineral. L-Glutamic acid and GABA are also commonly distributed in edible mushrooms. The fact that mushrooms accumulate GABA suggests the existence of GAD. However, the enzyme property of mushroom GAD has not been reported. In the present study, we tried to evaluate the property of Flammulina veltipes GAD, and the purification and characterization of enzyme is also investigated. [Methods and Results] Mushroom (fruit-body of Flammulina veltipes) used in this study was purchased in local market. GAD activity was determined by formation of GABA from L-glutamic acid in the presence of pyridoxal-5’- phosphate (PLP). The activity of enzyme was determined semi-quantitatively by color intensity of GABA on TLC analysis. Fruit-body was crushed and then centrifuged to separate supernatant and precipitate. To investigate the location of GAD, both supernatant and precipitate were subjected to enzyme reaction after dialysis. The enzyme activity of precipitate is stronger than that of supernatant. The formation of GABA was observed between pH 4 and 6 and the maximum color intensity of GABA was observed at pH 6. However, GAD activity was lost after dialysis for overnight against buffer of pH 6-11. These results suggest that GAD from Flammulina veltipes is stable at pH 4-5 in spite of its optimum pH for GABA production is around 6.

Gamma-Amino Butyric Acid (GABA), a four-carbon non protein amino acid, is widely distributed in nature and acts as the major suppressive neurotransmitter in the mammalian central nervous system. Recently, GABA has been reported to have several physiological functions such as antihypertensive, diuretic, relaxing and antidiabetic effects. Due to these unique biological functions, GABA has been used as functional ingredients for functional foods. Glutamic Acid Decarboxylase (GAD), which catalyzes decarboxylation of L-glutamic acid to GABA, has been purified from mammals, higher plants, and some microorganisms and their properties have already been reported. On the other hand, mushrooms are commonly appreciated as healthy food due to their nutritional properties, such as low calorie, rich in fiber, vitamin and mineral. L-Glutamic acid and GABA are also commonly distributed in edible mushrooms. The fact that mushrooms accumulate GABA suggests the existence of GAD. However, the enzyme property of mushroom GAD has not been reported. In the present study, we tried to purify and characterize the property of Flammulina veltipes. [Methods and Results] Mushroom (fruit-body of Flammulina veltipes) used in this study was purchased in local market. GAD activity was determined by formation of GABA from L-glutamic acid in the presence of pyridoxal-5’š- phosphate (PLP). The GAD activity was determined by the formation of GABA from L-glutamic acid. Fruit- body was crushed and then centrifuged to separate supernatant and cell debris. To investigate the localization of GAD, both supernatant and precipitate were subjected to enzyme reaction after dialysis. The cell debris showed stronger GAD activity than that of supernatant. The formation of GABA was observed between pH 4 and 6 and the maximum GAD activity was observed at pH 6. However, GAD activity was lost after dialysis for overnight against buffer of pH 6-11. These results suggest that GAD from Flammulina veltipes is stable at pH 4-5 in spite of its optimum pH for GABA production is around 6.