Abstract
Glutamic acid decarboxylase (GAD) [EC 4.1.1.15], an enzyme involved in accumulation of GABA by edible mushrooms, was purified from fruiting bodies of Grifola frondosa, and its properties were characterized. The GAD enzyme was purified 11.9-fold, with a yield of 1.24%, and showed a single band on SDS-PAGE. The molecular mass of purified GAD was 42 kDa based on SDS-PAGE and 97 kDa based on HPLC-GPC. These results indicate that the enzyme consists of 2 identical subunits. Maximum activity was observed at 37℃ at a pH value of 3.5. The enzyme was stable at 37℃ for 30 min and in the pH range 2.5-5.5. GAD isolated from G. frondosa was specific for _L-glutamate. The K_m and V_<max> of the enzyme were calculated to be 7.5 mM and 450 μmol min^<-1>, respectively. The enzyme activity was strongly inhibited by HgCl_2 and AgNO_3 (0% and 32% of activity in the absence of inhibitors, respectively).
