China
Africa
Explore chapters and articles related to this topic
Consideration of Glutamine Synthetase as a Multifunctional Protein
Published in James F. Kane, Multifunctional Proteins: Catalytic/Structural and Regulatory, 2019
The amino acid glutamine is not only essential for protein synthesis but also as a precursor for other nitrogen-containing compounds in cells. The enzyme responsible for glutamine production, glutamine synthetase, is widely distributed in microorganisms, plants, and animals and catalyzes the conversion of glutamate and ammonia to glutamine with the cleavage of ATP to ADP and Pi Glutamine synthetase occupies a central position in cell physiology, because it forms an intersection of pathways for carbon metabolism, ammonia assimilation, amino acid synthesis, and the availability of glutamate and glutamine as precursors for other cell constituents. Many microorganisms use glutamate synthase, which converts glutamine and α-ketoglutarate to two glutamates, as the primary route for glutamate production. For these organisms, glutamine synthetase has the interesting physiological role of using glutamate as a substrate to make glutamine, which serves as a product for other cell metabolism and as a precursor for producing more glutamate. In this role, glutamine synthetase is in a cyclic reaction necessary for making one of its substrates.
The Azolia-Anabaena Symbiosis
Published in Peter M. Gresshoff, Molecular Biology of Symbiotic Nitrogen Fixation, 2018
Recently, Meeks et al.79 have confirmed that symbiotic Anabaena releases a substantial portion of its newly fixed nitrogen as ammonium. The authors showed that the nitrogen assimilation is conducted by the glutamine synthetase-glutamate synthase (GS/GOGAT) pathway with little or no synthesis of glutamate by glutamate dehydrogenase (GDH). The little biosynthetic activity of GDH in the isolated Anabaena indicated that all of GDH activity is associated with the hair cells of the cavity. This suggestion has been confirmed by other workers.33,80 It was also shown that N2-fixation and NH4+ assimilation were not tightly coupled as they are in free-living cyanobacteria.81,82 The release of ammonium supports the idea that GS, the initial enzyme of the primary ammonium assimilatory pathway, is repressed in symbiotic Anabaena.83,84
Glutamine Synthetase
Published in Elling Kvamme, Glutamine and Glutamate in Mammals, 1988
Glutamine participates in a number of amide and amine transfer reactions; in addition, glutamine is a constituent of most proteins (Figure 1). The amide nitrogen of glutamine is used for the synthesis of nitrogen 3 and 9 of the purine ring, the amide of NAD+, asparagine amide, nitrogen 1 of the imidazole ring of histidine, the pyrrole nitrogen of tryptophan, the amino groups of glucosamine-6-phosphate, guanine, cytidine and p-aminobenzoate, and carbamyl phosphate. Carbamyl phosphate is in turn used for the synthesis of urea, arginine, and nitrogen I of the pyrimidine ring.3,5 In these reactions glutamine seems to play a role that could conceivably have been fulfilled by ammonia. However, ammonia is toxic to many animal tissues, particularly the central nervous system (CNS). It may be that for thermodynamic reasons ammonia cannot bind easily to most enzymes that catalyze nitrogen incorporation reactions. On the other hand, glutamine provides a “handle” that allows easy binding to glutamine amidotransferases. Glutamine thus serves as a nontoxic store of easily transferred nitrogen and of glutamate. In man (and probably in the higher apes) glutamine participates in a unique detoxification reaction: phenylacetic acid (derived from phenylalanine) is coupled with glutamine to form phenylacetylglutamine, which is excreted in the urine in large amounts.6 Certain microorganisms and plants contain glutamate synthase, an enzyme that reductively transfers the amide nitrogen of glutamine to α-ketoglutarate (2-oxoglutarate) to yield glutamate (Figure 1).7,8 Apparently, the combined action of glutamine synthetase and glutamate synthase is more efficient at fixing low levels of ammonia into glutamate than is glutamate dehydrogenase. Glutamate synthase has not been detected in mammalian tissues but O’ Donovan and Lotspeich9 have suggested (based on studies with l-[amide-15N]glutamine) that kidney cortex preparations can catalyze the transfer of the amide nitrogen of glutamine to pyruvate, oxaloacetate, and α-ketoglutarate without prior formation of free ammonia. The exact mechanism remains to be elucidated. Glutamine is a major fuel of the small intestine,10 bone,” human diploid fibroblasts,12 HeLa cells,13 and possibly of the brain14 (see Chapter 10). In addition glutamine is a major source of urinary ammonia (see below) while oxidation of the carbon skeleton provides an important source of energy.15
Birth weight related essential, non-essential and conditionally essential amino acid blood concentrations in 12,000 breastfed full-term infants perinatally
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2020
Penelope D. Manta-Vogli, Kleopatra H. Schulpis, Yannis L. Loukas, Yannis Dotsikas
CEAAs (Table 1) can be synthesized in adequate amounts by the organism, but in cases of preterm birth, LBW or perinatal nutritional problems that impose parenteral nutrition their quantities that can be synthesized could be quite limited [3]. Perinatally, Gln is one of the most important amino acids for energy production and gut maturity [38]. Additionally, Glu + Gln are the main precursors for intestinal Arg synthesis in neonates [30]. In this metabolic pathway, the enzymes phosphate-dependent glutaminase, OAT, arginosuccinate synthetase (ASS), arginosuccinate lyase (ASL) and aspartate aminotransferase, are widely distributed in animal tissues, whereas CPS I, OCT and N-acetyl glutamate synthase are restricted in the liver and intestinal mucosa. Proline oxidase is present mainly in the small intestine, liver and kidneys but P-5-C is located almost exclusively in the intestinal mucosa, with only trace amounts in other tissues [30].
Effect of UV-B radiation on amino acids profile, antioxidant enzymes and lipid peroxidation of some cyanobacteria and green algae
Published in International Journal of Radiation Biology, 2020
Hani Saber, Mostafa M. El-Sheekh, Aml Ibrahim, Eman A. Alwaleed
From the results, it could be concluded that the amino acids in microalgae were changed in response to UV exposure. Alanine was increased after UV-B radiation exposure on Nostoc carneum, Microcystis aeruginosa, and the marine alga Microcystis. Glutamatic increased in Planktothrix cryptovaginata, Microcystis aeruginosa, Scenedesmus acutus and Nostoc carneum. Similar results were recorded in Ulva lactuca and Pterocladia capillacea, where alanine and glutamic acid increased after UV-B irradiation (Noaman et al. 2016). The marked increase of alanine after exposure of algae to UV-B might occur due to an enhancement of the alanine aminotransferase activity (Döhler et al. 1997). Moreover, alanine decreased in Planktothrix cryptovaginata, and Scenedesmus acutus and Glutamatic decreased in the marine alga Microcystis. Similar results were obtained when exposed Sargassum hornschuchii to UV-B radiation (Noaman et al. 2016), which was discussed by the damaging effect on the uptake of inorganic nitrogen and nitrogen metabolism (Döhler 1992). Otherwise, the results found with UV sources regarding glutamine and glutamate indicate a different influence on the glutamine synthetase/glutamate synthase (GS/GOGAT) system (Döhler et al. 1997).