There are two forms of glutamic acid decarboxylases (GADs) that exist in brain: GAD-65 (also known as GAD2) and GAD-67 (also known as GAD1, GAD or SCP). GAD-65 and GAD-67 are members of the group II decarboxylase family of proteins and are responsible for catalyzing the rate limiting step in the production of GABA (gamma-aminobutyric acid) from L-glutamic acid. Although both GADs are found in brain, GAD-65 localizes to synaptic vesicle membranes in nerve terminals, while GAD-67 is distributed throughout the cell. GAD-67 is responsible for the basal levels of GABA synthesis. In the case of a heightened demand for GABA in neurotransmission, GAD-65 transiently activates to assist in GABA production. As a member of the group II decarboxylase family, GADL1 (Glutamate decarboxylase-like protein 1) is a 521 amino acid protein that utilizes pyridoxal phosphate as a cofactor for its carboxylase activity. There are two isoforms of GADL1 that exist as a result of alternative splicing events.