Glutamate decarboxylase

L-Glutamate decarboxylase (GAD, EC4.1.1.15) which catalyzes the conversion of Lglutamate to γ-aminobutyric acid (GABA), an important inhibitory neurotransmitter, is a specific marker for GABAergic neurons and their processes.^1-4 Although GABA and GAD were originally believed to exist exclusively in the central nervous system (CNS) of the vertebrate⁵, with more sensitive methods GABA and GAD activity has been detected in glia and nonneural tissues such as the kidney, heart, liver, pancreas, adrenal medulla, and blood vessels.^6-16 However, little is known with certainty about the properties of glial or nonneural GAD. Contrary to the glial GAD, the neuronal GAD has been purified to homogeneity from several species including the mouse,¹⁷ rat,^18,19 bovine,²⁰ catfish,²¹ and human²² and its properties have also been extensively characterized.^23-27In a ddition, specific polyclonal and monoclonal antibodies against the neuronal GAD have also been obtained and characterized'^28-31 and applied extensively for immunochemical and immunocytochemical studies of GAD in the vertebrate (for a review see References 2 to 4 and 32). In this review, the authors would like to cover the purification procedures, the criteria of purity, and the basic kinetic, physical, and immunochemical properties of GAD in addition to their application of the identification of GABAergic neurons and their projections.