Influence of total nitrogen, asparagine, and glutamine on MCA tumor growth in the Fischer 344 rat.
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Aspartic acid
Glutamic acid
Asparagine synthetase
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Asparagine synthetase
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Nitrogen assimilation is a vital process controlling plant growth and development. Inorganic nitrogen is assimilated into the amino acids glutamine, glutamate, asparagine, and aspartate, which serve as important nitrogen carriers in plants. The enzymes glutamine synthetase (GS), glutamate synthase (GOGAT), glutamate dehydrogenase (GDH), aspartate aminotransferase (AspAT), and asparagine synthetase (AS) are responsible for the biosynthesis of these nitrogen-carrying amino acids. Biochemical studies have revealed the existence of multiple isoenzymes for each of these enzymes. Recent molecular analyses demonstrate that each enzyme is encoded by a gene family wherein individual members encode distinct isoenzymes that are differentially regulated by environmental stimuli, metabolic control, developmental control, and tissue/cell-type specificity. We review the recent progress in using molecular-genetic approaches to delineate the regulatory mechanisms controlling nitrogen assimilation into amino acids and to define the physiological role of each isoenzyme involved in this metabolic pathway.
Asparagine synthetase
Glutamate synthase
Nitrogen Assimilation
Assimilation (phonology)
Amino acid synthesis
Metabolic pathway
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Vacuoles of internodal cells of Chara australis (or Chara corallina) were loaded with a 10 millimolar amount of various amino acids by a perfusion method and incubated under continuous light. After 20 to 24 hours, the cell sap was collected, and free amino acids in it and the rest of the cell (cytoplasm) were analyzed. The only amino acid metabolized completely was alanine. About 40 to 80% of the aspartic acid, glutamine, serine, and glycine were metabolized, whereas less than 30% of the threonine, asparagine, isoasparagine, isoleucine, phenylalanine, gamma-aminobutyric acid, lysine, and arginine were metabolized. The figure for glutamic acid fluctuated between 10 and 100%. The main metabolites of alanine were glutamine, glycine and ammonia, which accumulated in the vacuole. Alanine utilization was not affected by l-methionine-d,l-sulfoximine or azaserine, but was strongly inhibited by aminooxyacetate. The cell extract contained enough alanine aminotransferase activity to account for the rate of alanine metabolism.
Alanine
Amino acid synthesis
Azaserine
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Chara
Glutamic acid
Isoleucine
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Abstract Background Insect cells can serve as host systems for the recombinant expression of eukaryotic proteins. Using this platform, the controlled expression of 15 N/ 13 C labelled proteins requires the analysis of incorporation paths and rates of isotope-labelled precursors present in the medium into amino acids. For this purpose, Spodoptera frugiperda cells were grown in a complex medium containing [U- 13 C 6 ]glucose. In a second experiment, cultures of S. frugiperda were grown in the presence of 15 N-phenylalanine. Results Quantitative NMR analysis showed incorporation of the proffered [U- 13 C 6 ]glucose into the ribose moiety of ribonucleosides (40 – 45%) and into the amino acids, alanine (41%), glutamic acid/glutamine (C-4 and C-5, 30%) and aspartate/asparagine (15%). Other amino acids and the purine ring of nucleosides were not formed from exogenous glucose in significant amounts (> 5%). Prior to the incorporation into protein the proffered 15 N-phenylalanine lost about 70% of its label by transamination and the labelled compound was not converted into tyrosine to a significant extent. Conclusion Growth of S. frugiperda cells in the presence of [U- 13 C 6 ]glucose is conducive to the fractional labelling of ribonucleosides, alanine, glutamic acid/glutamine and aspartic acid/asparagine. The isotopolog compositions of the ribonucleosides and of alanine indicate considerable recycling of carbohydrate intermediates in the reductive branch of the pentose phosphate pathway. The incorporation of 15 N-labelled amino acids may be hampered by loss of the 15 N-label by transamination.
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Alanine
Aspartic acid
Transaminase
Glutamic acid
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The keto acid 2-oxo-4[methylthio]butanoic acid (OMTB) is an intermediate in the conversion of synthetic feed grade methionine sources to L-methionine in vivo in poultry and other animals. Because methionine sources are utilized by the chick with considerably less than 100% efficiency as sources of L-methionine, it is important to determine what metabolic process may limit the utilization of these sources. Because OMTB is converted to L-methionine by transamination, a study was conducted to determine which amino acids might serve as nitrogen donors in the conversion of OMTB to L-methionine in the chicken. Dialyzed tissue homogenates, mitochondria, and cytosol from liver, kidney, intestine, and skeletal muscle were incubated with OMTB and individual L-amino acids (isoleucine, leucine, valine, glutamic acid, aspartic acid, alanine, glutamine, asparagine, and phenylalanine) and the methionine that accumulated was determined by ion exchange chromatography. Tissues differed in the conversion of OMTB to methionine: kidney was most active, liver and intestinal mucosa were intermediate, and skeletal muscle had lowest activity. All amino acids supported methionine synthesis. Branched-chain amino acids and glutamic acid were the most effective substrates in tissue cytosols except in intestinal mucosa, in which asparagine was also effective. The preferred substrates in mitochondria were glutamate in liver mitochondria, isoleucine and alanine in kidney mitochondria, and branched-chain amino acids and glutamic acid in skeletal muscle mitochondria. All amino acids except alanine supported methionine synthesis from OMTB in mitochondria of intestinal mucosa. We conclude that a wide variety of amino acids can serve as substrates for transamination of OMTB in the chicken, and that the availability of nitrogen donors is unlikely to be a limiting factor in the conversion of OMTB to methionine.
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ABSTRACT The transepithelial electrical potential difference across the isolated midgut of Bombyx mori larvae is dependent on the presence of potassium and is unaffected by the addition of hexoses to perfusion media, whereas it is enhanced by alanine, aspartic acid, glutamic acid and the corresponding 2-oxoacids, glutamine and malate. The midgut enzyme profile indicates that the substrates for the tricarboxylic acid cycle are supplied mainly by amino acid metabolism via transaminases. Accordingly, aminoxyacetate drastically reduces the intestinal transepithelial electrical potential difference stimulated by amino acids. Measurement of the free amino acid concentration in the lumen content, intestinal cells and haemolymph shows that glutamic acid, asparagine and glutamine are accumulated in the cell, whilst the haemolymph is enriched with basic amino acids and with glycine, alanine, serine and tyrosine, the major components of the silk fibroin. Therefore, amino acid metabolism directly related to the tricarboxylic acid cycle seems to be the primary source of energy for the potassium pump activity inB. mori midgut.
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Hemolymph
Glutamic acid
Aspartic acid
Tricarboxylic acid
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Abstract Cultured mammalian cells can synthesize both glutamic acid and glutamine in amounts sufficient for growth. The necessary conditions are (a) a sufficiently high population density, approaching that of a saturated culture, and (b) glutamine synthetase activity sufficiently high to utilize the newly formed glutamic acid effectively. Three strains of rat tumor cells in culture had widely varying biosynthetic capacities for asparagine, with corresponding differences in the minimum population densities permitting growth and in the precursors necessary. At extremely high population densities the 3-methyl-4-dimethylaminoazobenzene-induced carcinoma cell could grow in the absence of both aspartic acid and asparagine, the carbon skeleton then deriving from glucose and glutamine. The Jensen sarcoma cell could also synthesize aspartic acid; however, exogenous aspartic acid had to be provided in order to permit growth, the minimum effective concentration varying inversely with the population density. Although the Walker 256 cell could also synthesize aspartic acid and could transport an exogenous supply into the cell, the strain here studied would not grow under any conditions in the absence of preformed asparagine, indicative of an almost complete block in asparagine synthesis from aspartic acid and glutamine. Possible determinants of these population-dependent requirements are discussed.
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SYNOPSIS The amino acid composition of the acid soluble fraction of Euglena gracilis was determined from cells grown in 4 different culture media. Glutamic acid is the major free amino acid. Hydrolysis of this fraction increases the amount of free amino groups, the major amino acids found are then glutamic acid, aspartic acid, glycine and arginine. The pattern of amino acid distribution is similar in all 4 culture media. L‐arginyl‐L‐glutamine was isolated and identified in extracts from all 4 culture conditions. It was shown to be a metabolic intermediate by radioactivity chase experiments.
Euglena gracilis
Glutamic acid
Aspartic acid
Euglena
Amino Acid Analysis
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