Enzymes Involved in Glutamatergic and GABAergic Neurotransmission

Abstract

Publisher Summary This chapter describes the important enzymes of the glutamate and gamma aminobutyric acid (GABA) metabolism, their cellular compartmentation, and their possible involvement in neurotransmission. The formation of glutamate and GABA is closely related to glucose metabolism. The important enzymes involved in glutamate metabolism in the central nervous system (CNS) are aminotransferases, glutamate dehydrogenase, glutamine synthetase, and phosphate-activated glutaminase. The enzyme aspartate aminotransferase (AAT) is one of the most active enzymes in the brain, with activity levels comparable to those of some enzymes of the glycolytic or respiratory cycles. Glutamine synthetase (Gs) is considered as a crucial enzyme for the maintenance of nitrogen homeostasis because it replenishes L-glutamine, an amino acid that is a constituent of most proteins and that serves as a nitrogen source for a variety of important metabolites. Important enzymes of the glutamate metabolism are at least strongly enriched in astrocytes. These are glutamate dehydrogenase and glutamine synthetase. The enzymatic formation and destruction of the inhibitory amino acid transmitter GABA form a short annex to the tricarboxylic acid (TCA) cycle in the brain, providing an alternative route from α -ketoglutarate to succinate. Glutamate decarboxylase, which releases GABA from glutamate, is a marker enzyme for GABAergic neurons.