Catalyzes the production of GABA. H(+) + L-glutamate = 4-aminobutanoate + CO2 Homodimer. Expressed in the head (at protein level). Expressed in early embryonic development (4-8 h) and in all later developmental stages. RNAi-mediated knockdown in 5-HT1B+ neurons leads to dis-inhibition of male aggressive behavior. Belongs to the group II decarboxylase family.