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At least 613 records · Page 34Linked to original sources
PubMed1987

The effects of inhibitors of sulphur-containing amino acid metabolism on the growth of Trichomonas vaginalis in vitro.

A range of inhibitors of enzymes catalysing the metabolism of sulphur-containing amino acids were tested for efficacy against Trichomonas vaginalis in vitro. Sinefungin, tubercidin, ara A, bithionol, hexachlorophene, dichlorophene and 5-azacytidine were found to be effective antitrichomonal agents. Combinations of any two of these inhibitors were, in most cases, no more effective than one inhibitor used alone, but marked synergy was apparent with monothioglycerol and methionine. None of the inhibitors investigated was as potent as metronidazole, the drug of choice for the treatment of trichomoniasis.

Amino Acids, Sulfur↗
PubMed1993

An animal model for the study of amino acid metabolism in uremia and during peritoneal dialysis.

We tried to determine the suitability of the rabbit as an animal model to study amino acid (AA) metabolism in continuous ambulatory peritoneal dialysis. We also measured the effect of intraperitoneal (ip) infusion of AA on blood AA changes and food consumption. Plasma AA levels were measured in 10 normal rabbits after an overnight fasting and 30, 60, and 120 minutes after a meal. Following these baseline observations, rabbits were randomly divided into two groups. One group of five rabbits was made uremic after surgical partial nephrectomy, whereas the remaining (controls) underwent sham operations. Two weeks after the induction of uremia we measured the effect of chronic renal failure on fasting and postprandial (30, 60, 120 minutes) plasma AA levels. Upon the completion of the second experiment (4 weeks after the induction of uremia) we studied the effect of an ip AA on plasma AA profile 1, 2, 4, and 6 hours after the infusion in both uremic and control rabbits. We also measured the food intake in all experiments. The results of our experiments showed the following: 1. plasma AA in the rabbits decreased after induction of chronic renal failure and increased after food ingestion and ip infusion of AA solution; 2. neither induction of uremia nor ip AA infusion have an effect on food consumption; 3. the majority of the alterations in plasma AA levels we observed in the uremic rabbits were similar to those observed in humans, indicating that the rabbit may be a suitable model for the study of AA metabolism in chronic renal failure and during peritoneal dialysis.

Amino Acids↗
PubMed2000

Protein and amino acid metabolism during and after exercise and the effects of nutrition.

Sustained dynamic exercise stimulates amino acid oxidation, chiefly of the branched-chain amino acids, and ammonia production in proportion to exercise intensity; if the exercise is intense enough, there is a net loss of muscle protein (as a result of decreased protein synthesis, increased breakdown, or both); some of the amino acids are oxidized as fuel, whereas the rest provide substrates for gluconeogenesis and possibly for acid-based regulation. Protein balance is restored after exercise, but no hypertrophy occurs with habitual dynamic exercise. Resistance exercise causes little change in amino acid oxidation but probably depresses protein synthesis and elevates breakdown acutely. After exercise, protein synthesis rebounds for </=48 h, but breakdown remains elevated, and net positive balance is achieved only if amino acid availability is increased. There is no evidence that habitual exercise increases protein requirements; indeed protein metabolism may become more efficient as a result of training.

Amino Acids↗
PubMed1985

Regional and subcellular distribution of enzymes of branched-chain amino acid metabolism in brains of normal and diabetic rats.

Branched-chain-amino-acid:alpha-ketoglutarate transaminase and branched-chain alpha-ketoacid dehydrogenase have been assayed in brains of control and of streptozotocin-induced diabetic rats. Enzyme activities were measured in five distinct regions of the brain: cerebellum, pons + medulla, midbrain, thalamus + hypothalamus, and telencephalon. Subcellular distribution of these enzymes in whole brain was assessed by fractionating brain homogenate into cytoplasm, free mitochondria, and synaptosomes. The following enzymes were used as markers: lactate dehydrogenase for cytoplasm, glutamate dehydrogenase for mitochondria, and glutamate decarboxylase for synaptosomes. The activity of the branched-chain amino acid transaminase in all brain regions was considerably higher than that of the branched-chain alpha-ketoacid dehydrogenase. While the highest activity of the transaminase occurred in brain-stem regions, the highest activity of the dehydrogenase was present in cerebellum and telencephalon. Diabetes did not affect the activity of the transaminase, but it caused a decrease in the total activity of the dehydrogenase in midbrain and in thalamus + hypothalamus. The transaminase was localized in the cytoplasmic fraction of whole brain, while the dehydrogenase was enriched in the free mitochondria.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1977

[Studies on the protein and amino acid metabolism of laying hens receiving 15N-labelled casein. 5. 15N incorporation into different blood fractions and into the amino acids lysine, histidine and arginine contained in these fractions].

4 colostomizted laying hens were fed 15N labelled casein as a sole source of protein for a period of 6 days. The birds were slaughtered 2 or 6 days after receiving 15N dose. The blood was separated into corpuscular blood components and blood plasma. Then, the amount and content of nitrogen in the blood, the blood fractions and in the amino acids lysine, histidine and arginine and the excess of 15N atom% (15N') were estimated. The average N concentrationin the blood was 3.8%. The crude protein in the blood corpuscles contained 8.7% lysine, 7.1% histidine and 6.4% arginine; the corresponding values for crude plasma protein were 6.3%, 2.2% and 5.7%. The 15N atom% in blood nitrogen was found to be lower in the hens slaughtered 144 hrs after receiving the last 15N dose than in the birds already slaughtered after 48 hrs. The same trend was found for the plasma proteins. The level of excess 15N atom% in the blood corpuscles increased with the length of time elapsing after the withdrawal of 15N casein (over the period of time investigated); a decrease of excess 15N atom% in plasma lysine was noted, however, for the investigated period of time after the last 15N dose. In the corpuscular blood components a higher level of 15N atom% was usually found in histidine relative to that in lysine and arginine; it was higher in the hens slaughtered 6 days after receiving the final 15N dose than in the hens killed 2 days after administration of the last 15N dose.

Amino Acids↗
PubMed1989

Amino Acid Metabolism of Lemna minor L. : IV. N-Labeling Kinetics of the Amide and Amino Groups of Glutamine and Asparagine.

A serious limitation to the use of N(O,S)-heptafluorobutyryl isobutyl amino acid derivatives in the analysis of (15)N-labeling kinetics of amino acids in plant tissues, is that the amides glutamine and asparagine undergo acid hydrolysis to glutamate and aspartate, respectively, during derivatization. This led us to consider an alternative procedure (G Fortier et al. [1986] J Chromatogr 361: 253-261) for derivatization of glutamine and asparagine with N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide in pyridine. Gas chromatography-mass spectrometry (electron ionization) yielded fragment ions (M-57) of mass 417 and 431 for the [(14)N]asparagine and [(14)N]glutamine derivatives, respectively, suitable for monitoring unlabeled, single-(15)N- and double-(15)N-labeled amide species from the ion clusters at mass to charge ratio (m/z) 415 to 423 for asparagine, and m/z 429 to 437 for glutamine. From separate analyses of the specific isotope abundance of the amino-N groups of asparagine and glutamine as their N-heptafluorobutyryl isobutyl derivatives, the specific amide-[(15)N] abundance of these amino acids was determined. We demonstrate that this approach to (15)N analysis of the amides can yield unique insights as to the compartmentation of asparagine and glutamine in vivo. The ratios of unlabeled:single-(15)N:double-(15)N-labeled species are highly diagnostic of the relative sizes and turnover of metabolically active and inactive pools of the amides and their precursors. Kinetic evidence is presented to indicate that a significant proportion (approximately 10%) of the free asparagine pool may be metabolically inactive (vacuolar). If the amide group of asparagine is derived exclusively from glutamine-amide, then asparagine must be synthesized in a compartment of the cell in which both glutamine-amide and aspartate are more heavily labeled with (15)N than the bulk pools of these amino acids. This compartment is presumably the chloroplast. The transaminase inhibitor aminooxyacetate is shown to markedly inhibit amino acid synthesis; several amino acid pools accumulated in the presence of aminooxyacetate and [(15)N]H(4) (+) are (14)N-enriched and must be derived primarily from protein turnover.

Journal Article↗
PubMed1992

[The dibasic amino acid metabolic disorders].

The ornithine transcarbamylase deficiency (OTCD), arginase deficiency (ARD), Hyperornithinemia-Hyperammonemia-Homocitrullinuria (H.H.H) syndrome and Lysinuric protein intolerance (LPI) are characterized by the accumulation of the precursors of urea, principally ammonia because of the abnormal metabolism of ornithine, arginine and lysine which are the dibasic amino acid. We mainly described the recent knowledge for these disease and introduced the great advancement of the molecular biology in this field which makes us to give an early diagnosis for these disease to have an early treatment.

Amino Acid Metabolism, Inborn Errors↗
PubMed1988

Intravenously infused carnitine: influence on protein and branched-chain amino acid metabolism in starved and parenterally fed rats.

We studied the effect of intravenously infused carnitine (34 mumol.100 g-1.d-1) on protein and branched-chain amino acid (BCAA) metabolism in rats either starved for 3 d or parenterally fed for 7 d. Carnitine infusion did not significantly affect nitrogen balance, protein content of liver and muscle, plasma concentrations of BCAA and branched-chain keto acid, or leucine oxidation and incorporation into liver and muscle proteins of either starved or fed rats. Despite a two- to threefold increase in plasma carnitine level, tissue concentrations of carnitine and its acyl-derivatives were not significantly affected by carnitine infusion. Of the amount of carnitine infused, 91% was lost in the urine of starved rats and 87% in the urine of fed rats. We conclude that intravenous carnitine infusion does not affect protein and BCAA metabolism and that this lack of effect may be related to the failure of carnitine infusion to enrich tissue pools of carnitine.

3-Hydroxybutyric Acid↗
PubMed1996

In vivo amino acid metabolism of gut and liver during short and prolonged starvation.

During starvation, splanchnic organs are proportionally more affected by protein loss than other organs. Amino acid membrane transport is one of the regulating mechanisms of protein turnover, but until now in vivo data were lacking. To study in vivo phenylalanine and tyrosine membrane transport and protein turnover in splanchnic organs, a primed continuous infusion of L-[2,6-3H]phenylalanine was given to control rats (postabsorptive) and after short (40 h) and prolonged (112 h) starvation. Data were analyzed using a three-compartment model previously used in muscle membrane transport studies. Inward and outward amino acid plasma-tissue membrane transport rates in both the liver and gut were upregulated after prolonged starvation. Metabolic shunting of phenylalanine and tyrosine increased in the gut but decreased to zero in the liver after prolonged starvation. In conjunction with this, gut and liver protein turnover increased after prolonged starvation. In the liver the net uptake of gluconeogenic precursors also increased, indicative for increased gluconeogenesis. The observed changes in amino acid metabolism in both splanchnic organs after prolonged starvation may reflect an adaptation of the gut and liver to nutritional deprivation and could be of benefit during refeeding.

Acute Disease↗
PubMed1985

Amino acid metabolism by perfused rat hindquarter. Effects of insulin, leucine and 2-chloro-4-methylvalerate.

Hindquarters from starved rats were perfused without substrates but in the presence of an O2- and CO2-carrying perfluorocarbon emulsion to evaluate principally the metabolism of individual endogenous and protein-derived amino acids by this muscle preparation. This experimental model was shown, by a battery of metabolite measurements, to maintain cellular homoeostasis for at least 2h. The net appearance of most amino acids closely approximated their frequency of occurrence in muscle proteins, showing that they are not significantly metabolized. Exceptions were the branched-chain amino acids, methionine and those amino acids that are interconvertible with intermediates of the citrate cycle and pyruvate through coupled transaminations. The evidence indicates that only valine, isoleucine, aspartate and probably methionine can be catabolized by skeletal muscle to provide carbon precursors for glutamate/glutamine and alanine that are formed de novo by protein-catabolic muscle. The protein-sparing effects of insulin and leucine were confirmed. Although each decreased proteolysis and the net appearance of free amino acids, they were generally without effect on the ratios of amino acids formed. 2-Chloro-4-methylvalerate selectively stimulated the removal rate for the branched-chain amino acids, confirming the idea that the branched-chain oxo acid dehydrogenase normally limits the rate of their oxidation by muscle. It is also concluded that, since alanine was not formed in excess of that found in muscle proteins when no glucose was added as substrate, the excess of alanine (carbon) released from muscles in other studies is derived to a large extent, but not exclusively, from preformed carbohydrate.

Amino Acids↗