Catalyzes the production of GABA. H(+) + L-glutamate = 4-aminobutanoate + CO2 Homodimer. Associated to cytoplasmic vesicles. In neurons, cytosolic leaflet of Golgi membranes and presynaptic clusters (By similarity). Phosphorylated; which does not affect kinetic parameters or subcellular location. Palmitoylated; which is required for presynaptic clustering. Belongs to the group II decarboxylase family.