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Results for “AMINO ACID METABOLISM”

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PubMed1994

Measurement of amino acid metabolism derived from [1-13C]glucose in the rat brain using 13C magnetic resonance spectroscopy.

To clarify the unique characteristics of amino acid metabolism derived from glucose in the central nervous system (CNS), we injected [1-13C]glucose intraperitoneally to the rat, and extracted the free amino acids from several kinds of tissues and measured the amount of incorporation of 13C derived from [1-13C]glucose into each amino acid using 13C-magnetic resonance spectroscopy (NMR). In the adult rat brain, the intensities of resonances from 13C-amino acids were observed in the following order: glutamate, glutamine, aspartate, gamma-aminobutyrate (GABA) and alanine. There seemed no regional difference on this labeling pattern in the brain. However, only in the striatum and thalamus, the intensities of resonances from [2-13C]GABA were larger than that from [2,3-13C]aspartate. In the other tissues, such as heart, kidney, liver, spleen, muscle, lung and small intestine, the resonances from GABA were not detected and every intensity of resonances from 13C-amino acids, except 13C-alanine, was much smaller than those in the brain and spinal cord. In the serum, 13C-amino acid was not detected at all. When the rats were decapitated, in the brain, the resonances from [1-13C]glucose greatly reduced and the intensities of resonances from [3-13C]lactate, [3-13C]alanine, [2, 3, 4-13C]GABA and [2-13C]glutamine became larger as compared with those in the case that the rats were sacrificed with microwave. In other tissues, the resonances from [1-13C]glucose were clearly detected even after the decapitation. In the glioma induced by nitrosoethylurea in the spinal cord, the large resonances from glutamine and alanine were observed; however, the intensities of resonances from glutamate were considerably reduced and the resonances from GABA and aspartate were not detected. These results show that the pattern of 13C label incorporation into amino acids is unique in the central nervous tissues and also suggest that the metabolic compartmentalization could exist in the CNS through the metabolic trafficking between neurons and astroglia.

Amino Acids↗
PubMed1975

Amino acid metabolism in the chronically uremic rat.

The chronically uremic rat has been used as a model to study amino acid metabolism in uremia. Uremic rats fed low protein diets (6% casein) survived longer than uremic rats receiving either higher levels of dietary protein or a low protein diet supplemented with a mixture of nonessential amino acids. Alterations in plasma amino acid levels were observed in the uremic rats and were similar to those found in patients with renal failure. Plasma concentrations of citrulline, free tryptophan, glycine and the methylhistidines were increased and levels of serine, ornithine, lysine, total tryptophan, tyrosine, and the tyrosine-phenylalanine ratio were reduced. The metabolic basis of the altered tyrosine-phenylalanine ratio in plasma was studied. Tyrosine aminotransferase (TAT) and phenylalanine hydroxylase (PHL) activity were normal in the liver, but renal PHL activity of was decreased as compared to control rats. Tissue concentrations of citrulline were also found to be raised in liver and muscle of uremic rats. The activity of ornithine transcarbamoylase, was reduced in the liver and arginine synthetase activity was decreased in the kidneys of uremic rats. Thus elevated citrulline levels in uremic tissue appear to be caused by a decrease conversion of citrulline to arginine in the kidney. Preliminary studies of tryptophan metabolism in uremic rats have shown elevated brain levels of 5-hydroxyindoleacetic acid and increased hepatic tryptophan oxygenase activity. Increased plasma amine levels were associated with altered activities of monoamine oxidase and diamine oxidase in kidney and other tissues.

Amine Oxidase (Copper-Containing)↗
PubMed1992

[Molecular biological aspects of amino acid metabolizing enzymes].

This article briefly describes the molecular biological aspect of studies on some enzymes involved in amino acid metabolism. Aspartate aminotransferase is one most extensively studied enzyme. Together with its three dimensional structure, recent studies using site-directed mutagenesis have led to the understanding of its structure-function relationships. Successful cDNA cloning of other aminotransferase has enabled us to understand the degree of homology in amino acid sequence. cDNAs for several amino acid decarboxylases were also cloned. Genomic structures for the enzymes involved in urea cycle have been studied. These studies have provided a molecular basis for some hyperammonemias. Its is strongly anticipated that the understanding of other metabolic disorders may be promoted by further accumulation of molecular biological data on the relevant enzymes.

Amino Acid Sequence↗
PubMed2005

Amino acid metabolic routes in Trypanosoma cruzi: possible therapeutic targets against Chagas' disease.

Chagas' disease is a zoonosis caused by the parasite Trypanosoma cruzi, a haematic protozoan, transmitted by insects from the Reduviidae family. This constitutes a relevant health and socio-economic problem in the Americas, with 11 - 18 million people infected, and approximately 100 million people at risk. The therapeutic possibilities rely into two drugs, nifurtimox and benznidazole, that were discovered more than thirty years ago, and are mainly successful during the acute phase of the disease. In the majority of the cases the disease is diagnosed in the chronic phase, when the therapy is inefficient and the probability of cure is low. In addition, these drugs are highly toxic, with systemic side effects on patients. Trypanosoma cruzi has a metabolism largely based on the consumption of amino acids, mainly proline, aspartate and glutamate, which constitute the main carbon and energy sources in the insect stage of the parasite life cycle. These amino acids also participate in the differentiation process of the replicative non-infective form (epimastigote) to the non-replicative infective form (trypomastigote). In particular, the participation of proline in the intracellular differentiation cycle, which occurs in the mammalian host, was recently demonstrated. In addition, an arginine kinase has been described in T. cruzi and T. brucei, which converts free arginine to phosphoarginine, a phosphagen with a role as an energy reservoir. Arginine kinase seems to be an essential component of energy management during stress conditions. Taken together, these data indicate that amino acid metabolism may provide multiple as yet unexplored targets for therapeutic drugs.

Amino Acids↗
PubMed1994

Aromatic amino acid metabolism of neonatal piglets receiving TPN: effect of tyrosine precursors.

Low tyrosine solubility in total parenteral nutrition (TPN) solutions complicates meeting the aromatic amino acid needs of infants. This study compared the effectiveness of two tyrosine precursors to supply the aromatic amino acid needs of TPN-fed neonatal piglets with a control group in which total aromatic acid needs were met by the addition of phenylalanine (Phe). Eighteen 3-day-old male Yorkshire piglets (6/group) received TPN for 8 days by central line. The solution was supplemented with Phe or one of the following two tyrosine precursors: N-acetyltyrosine (N-AcTyr) or glycyltyrosine (GlyTyr). Aromatic amino acid metabolism, growth, and nitrogen utilization were measured. Average amino acid and energy intakes were 14.6 g.kg-1.day-1 and 1,050 kJ.kg-1.day-1. Nitrogen balance and utilization were significantly higher (P < 0.05) in piglets in the control Phe group and on the GlyTyr regimen. The high urinary excretion of N-AcTyr (65%) confirms its low bioavailability. Flux and oxidation were significantly higher (P < 0.05) in the Phe group. High plasma Phe levels and excretion of Phe catabolites, as well as the high plasma tyrosine in the GlyTyr group, indicate that current strategies employed to meet the aromatic amino acid needs of neonates on TPN need further refinement.

Amino Acids↗