Metabolism of glutamate

In 1958 Barker (20) isolated a red, heat stable, light labile, cofactor which was required for the metabolism of glutamate in cell-extracts of Clostridium tetanomorphum. Subsequently this cofactor was crystallized. X-ray crystallography identified Barker s cofactor as the coenzyme form of Vitamin B12 (15, 21). 

Van den Berg, C. J. and Garfinkel, D. A simulation study of brain compartments Metabolism of glutamate and related substances in mouse brain. Biochem. J. 23 211-218,1971. 

The biochemical roles of these processes The metabolism of glutamate and aspartate by the enterocytes provides not only ATP, via oxidation of the oxoacids, but can also be considered to be a detoxification process. Both glutamate and aspartate are neurotransmitters in the brain. If their concentrations in blood increase too much, they could interfere with the control of neurotransmitter levels in the brain with possible changes in behaviour or clinical problems (see below). One such phenomenon is Chinese Restaurant Syndrome , but there may be other problems, as yet not reparted. 

The reasons for the neurotoxic effects of ammonia have not yet been explained. It may disturb the metabolism of glutamate and its precursor glutamine in the brain (see p. 356). 

Several proteinogenic amino acids (see p. 60) have neurotransmitter effects. A particularly important one is glutamate, which acts as a stimulatory transmitter in the CNS. More than half of the synapses in the brain are glutaminergic. The metabolism of glutamate and that of the amine GABA synthesized from it (see below) are discussed in more detail on p.356. Glycine is an inhibitory neurotransmitter with effects in the spinal cord and in parts of the brain. 

The majority of synthetic reactions in mammalian cells takes place in the cytosol. The intramitochondrial localization of transhydrogenase excludes a direct participation in these anabolic processes. Substrate shuttle mechanisms (176, 177) are required to allow for the interaction between intra- and extramitochondrial nicotinamide nucleotide-dependent reactions. In the first instance transhydrogenase can be regarded to be functionally related to intramitochondrial NADP-linked reactions. A number of studies on isolated mitochondria have elaborated these relationships in some detail, in particular with regard to mitochondrial monooxygenation reactions and to the metabolism of glutamate and isocitrate. 

Fig. I. Metabolic map for synthesis and metabolism of glutamate and aspartate. AAT = aspartate aminotransferase AS = asparagine synthetase GAD = glutamic acid decarboxylase GDH = glutamate dehydrogenase GS = glutamine synthetase OAT = ornithine D-aminotransferase P5CDH = l-pyrroline-5-carboxylate dehydrogena.se PAG = phosphate-activated glutaminase PO = proline oxidase TCA = tricarboxylic acid.

Fig. 10. Synthesis and metabolism of glutamate and GABA in excitatory and inhibitory neurons in combination with astrocytic metabolism. The figure is modified from Kaneko and Mizuno (1994).

Kaneko T, Shigemoto R, Mizuno N (1988a) Metabolism of glutamate and ammonia in astrocytes an immunocytochemical study. Brain Res 457 160-164. 

Derouiche A (1996) Possible role of the Muller cell in uptake and metabolism of glutamate in the mammalian outer retina. Vis Res 36 3875-3878. 

Schousboe A (1981) Transport and metabolism of glutamate and GABA in neurons and glial cells. Int Rev Neurobiol 22 1-45. 

Glutamate metabolism. The metabolism of glutamate, including fates and sources of glutamate,... 

In 1937, Alexander E. Braunstein (1902-86), working in Moscow, was studying the metabolism of glutamate in muscles and made the interesting observation that when glutamate levels decrease so do lactate (anaerobic conditions) or pyruvate (aerobic conditions). In each case the concentrations of alanine increase. He had discovered the reversible transamination reactions that connect the intermediary metabolisms of proteins and carbohydrates. 

Geddes J W and Wood J D. (1984) Changes in the amino acid content of nerve endings (synaptosomes) induced by drugs that alter the metabolism of glutamate and y-aminobutyric acid / Neurochem 42, 16-24... 

Nicklas W J (1983) Relative Contributions of Neurons and Glia to Metabolism of Glutamate and GABA, in Glutamine, Glutamate, and GABA in the Central Nervous System (Hertz L., Kvamme E, McGeer E. G, and Schousboe A, eds.), pp. 219-231, Alan R Liss, New York... 

Schousboe A, Svenneby G, and Hertz L (1977) Uptake and metabolism of glutamate in astrocytes cultured from dissociated mouse brain hemispheres / Neurochem 29, 299. 

Shank R P and Baxter C F (1975) Uptake and metabolism of glutamate by isolated toad brains containing different levels of endogenous amino acids. / Neurochem 24, 641-646... 

An alternate pathway of metabolism of glutamic acid is by its decarboxylation to y-aminobutyric acid ilO-12). 

The following paths of bacterial metabolism of glutamic acid have now been demonstrated and some at least (marked ) are inhibited by crystal violet or one of the uncoupling agents such as sodium azide or 2,4-dinitrophenol ... 

There is no evidence that crystal violet will inhibit the internal metabolism of glutamic acid in Staph, aureus as it does in Strep, faecalis. If the amount of glutamic acid in the cells and external medium is determined before and after incubation of the cells with glutamic acid, there is an overall loss of glutamic acid on balance, but the extent of this loss appears to depend to a large degree upon the amount of glucose present in the incubation mixture. Table VI shows that if small amounts only of... 

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