For measurement of GAD activity, GBR (0.5 g) was ground
with 4 mL phosphate buffer (pH 5.8) in an ice bath for extraction
of the enzyme. The homogenate was centrifuged at
10,000 × g for 15 min at 4 °C by using refrigerated high speed
centrifuge (5810R, Eppendorf, SN, Germany). The resulting supernatant
was the crude GAD used for assay of the activity of
GAD. The reaction mixture which consisted of 0.1 mL of crude
enzyme liquid and 0.2 mL of substrate was incubated for 2 h
at 30 °C and then terminated by adding 0.2 mL of 0.2 mol L−1
borate buffer (pH 9.0) and 1 mL of 6% phenol and 0.4 mL of 9%
sodium hypochlorite. After intensive oscillation, the mixture
was put in boiling water for 10 min, then put in ice bath for
20 min.The mixture was analyzed colorimetric at 630 nm wavelength
to determine absorption value. The GAD activity was
defined with reference to a 1 mol of GABA produced at 30 °C
per min per unit dry weight (mol GABA min−1 g−1 DW).