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PubMed2001

Regulation of amino acid transporters by amino acid availability.

There is growing recognition that amino acid availability has profound effects on many aspects of cell function, including the control of membrane transport mechanisms, cell signalling, and gene expression. The precise mechanisms by which amino acids are able to elicit control over such diverse processes have become the focus of intense investigation recently. One particular area that has seen considerable advances is the molecular characterization of amino acid transporters, including members of the System A family, which are known to be regulated by amino acid supply. Recent developments concerning how cells sense and signal amino acid availability, and how this process influences the expression and function of amino acid transporters, are reviewed here. Elucidating the molecular mechanisms of these events will be important in clarifying how amino acid transporters might be regulated during altered nutritional states, and will be crucial for the design of new strategies aimed at improving nutritional support.

Amino Acid Transport Systems↗
PubMed1992

Utilization of organic acids and amino acids by species of the genus Bacillus: a useful means in taxonomy.

The type strains of 26 Bacillus species were investigated with respect to their capability to utilize 48 organic acids and 20 amino acids by using phenol red indicator plates and an amino acid analyzer, respectively. In addition, strains of Bacillus sphaericus were found to utilize many organic acids and amino acids in contrast to carbohydrates which are routinely checked. The results obtained indicated an individual utilization pattern for every species investigated, pointing to a useful taxonomic application of these tests for the genus Bacillus.

Amino Acids↗
PubMed1982

The intracellular acid-extractable (acid-soluble) amino acid pool in mammalian cells: 3 Competition for entry and its effects on incorporation into protein synthesis.

Competition studies have been carried out between normal and analogue amino acids with suspension cultured mammalian cells incubated, except for the competing amino acid, in normal medium. Although this produces less dramatic changes on uptake and incorporation than experiments performed in Krebs-Ringer solution, it has the advantage of obtaining data under more physiological conditions. A systematic survey with all the amino acids used has shown, in general, a non-specific interference for uptake into the acid-extractable pool, suggesting that a common pool-forming mechanism is involved. Individual differences in competitive behaviour probably arise from varying affinities of amino acids for the pool-forming mechanism, their ability to displace others from the pool, and the rate of their subsequent discharge, among other characteristics. Certain interactions appear exceptional, however, notably glycine and serine, which could be due to their linked metabolism. Incorporation of amino acids into protein of the same cells gave the anticipated high degree of specificity, but evidence is now presented that the amount of a particular labelled amino acid entering into protein depends not only on its absolute concentration in the medium, but also on its relative concentration. The results indicate that the effects of excesses of other amino acid is to reduce the probability with which the labelled species can be loaded by its own tRNA. This inhibition is of a non-specific nature.

Acids↗
PubMed1988

Influence of hyperinsulinaemia on intracellular amino acid levels and amino acid exchange across splanchnic and leg tissues in uraemia.

1. To examine whether insulin resistance in uraemia extends to amino acid metabolism, the effect of physiological hyperinsulinaemia on plasma amino acid concentrations was studied in 17 chronically uraemic and 28 healthy subjects by using the euglycaemic insulin clamp technique. 2. In six uraemic and seven control subjects, splanchnic and leg exchange of amino acids was quantified with hepatic and femoral venous catheterization, and in five uraemic and eight control subjects intracellular free amino acid concentrations were determined in muscle tissue obtained by needle biopsy. 3. In response to hyperinsulinaemia the plasma concentrations of all amino acids except alanine decreased by 10-50% in both uraemic and control subjects. Splanchnic alanine uptake declined by 20% and leg amino acid release tended to decrease in both groups. 4. The intracellular levels of all measured amino acids except alanine fell significantly and to a similar extent in uraemic and control subjects. 5. These results indicate that insulin-mediated alterations in regional amino acid exchange and in plasma and intracellular amino acid concentrations are similar in uraemic and control subjects. 6. It is concluded that tissue insensitivity to insulin in uraemia does not extend to uptake or release of amino acids and that resistance to insulin can be selective in its effect on different metabolic functions.

Adult↗
PubMed1981

The effect of intravenous amino acids on plasma amino acid concentration during total parenteral nutrition in infants with necrotizing enterocolitis.

Plasma aminograms of infants receiving total parenteral nutrition as part of the treatment for necrotizing enterocolitis were studied. Their ages varied from 2 to 60 days and their mean birth mass was 1 621 g (range 760-2 550 g). The intravenous administration of amino acids produced changes in plasma amino acid levels corresponding to the concentration of individual amino acid levels in the solution employed: higher levels of amino acids in the infusate produced increased plasma levels, whereas low plasma levels were obtained for amino acids not present or present in small amounts according to the solution used. The infants did not appear to suffer in any way, but the long-term effects still have to be evaluated. Pending further knowledge in this regard it is suggested that plasma amino acid levels should be maintained as near to normal values as possible. This could probably be achieved by the use of amino acid solutions specially formulated according to the amino acid profile of breast milk or the plasma amino acid profile of normal infants.

Amino Acids↗
PubMed1994

Differential regulation of insulin-like growth factor I (IGF-I) and IGF binding protein-1 messenger ribonucleic acids by amino acid availability and growth hormone in rat hepatocyte primary culture.

To determine the mechanisms involved in the nutritional regulation of insulin-like growth factor I (IGF-I) production and action, we studied the regulation of IGF-I and IGF-Binding Protein 1 (IGFBP-1) gene expression by GH and amino acid availability in rat hepatocyte primary culture. Hepatocytes were isolated by in situ collagenase perfusion and cultured on Matrigel in serum-free medium containing insulin and hydrocortisone. Rat GH (500 ng/ml) increased IGF-I messenger RNA (mRNA) abundance 6.9-fold at 24 h, as measured by Northern Blot using an IGF-I-specific riboprobe. In contrast, IGFBP-1 mRNA levels were decreased by 41% after 24 h of rat GH treatment. Hepatocytes were incubated for 24 h in three media differing in their amino acid concentrations: 0.2X, 1X, and 5X the normal rat plasma concentration. Amino acid deprivation (0.2X) decreased the abundance of IGF-I mRNAs (-56% after 24 h), whereas amino acid excess (5X) increased it (+70%) in comparison to the 1X medium. In contrast, amino acid deprivation increased IGFBP-1 mRNA abundance (+69%), whereas excess decreased it (-75%). Studies of the interaction between GH and amino acids, accomplished by the simultaneous manipulation of the two, suggest that each factor modulates the IGF-I mRNA and the IGFBP-1 mRNA and protein response to the other. We conclude that the IGF-I and IGFBP-1 genes are regulated in opposite ways by GH and amino acid availability. Our observations suggest that amino acids and GH regulate the production of IGF-I directly and exert indirect effects on IGF-I action by regulating the production of IGFBP-1.

Amino Acids↗
PubMed1976

Body weight change and nitrogen efficiencies in growing and adult rats fed diets containing various proportions of essential amino acids to total amino acids.

By using amino acid mixtures, a comparative study of nutritional effects of dietary essential amino acid proportions (EA %) has been made between growing and adult rats. Included were adult rats which were repleting from an 8-day protein depletion. It was shown that for growing rats at least 55 EA% was required to attain the maximum values of growth, nitrogen balance, nitrogen balance efficiency (nitrogen balance/nitrogen intake) and protein efficiency ratio (PER). The maximum biological value was found to be 94 at the 50 EA% level. For adult rats, at least 40 EA% was required to gain the maximum values of nitrogen balance and nitrogen balance efficiency under both maintenance and repletion. The biological values were found to be nearly 60 and 80 for maintenance and repletion, respectively.

Amino Acids↗
PubMed1999

Automated tandem mass spectrometry for mass newborn screening for disorders in fatty acid, organic acid, and amino acid metabolism.

Development of acylcarnitine and amino acid profiling using tandem mass spectrometry, and its application for use with dried blood specimens collected on filter-paper cards, has introduced an innovative new technology for detecting inborn errors of fatty acid, organic acid, and amino acid metabolism. From November 1, 1992 through June 30, 1999 we screened more than 700,000 newborns in Pennsylvania, Ohio, North Carolina, and Louisiana. We have prospectively detected 163 inborn errors of metabolism. Eighty-six patients have amino acid metabolism errors. Among them are phenylketonuria, hyperphenylalaninemia, maple syrup urine disease, and several urea cycle disorders. Thirty-two have organic acid metabolism errors, including glutaric aciduria type 1; 3-methylcrotonyl coenzyme A (CoA) carboxylase deficiency, propionic acidemia, methylmalonic acidemia, and 3-hydroxy-3-methylglutaryl-CoA lyase deficiency; and 45 have fatty acid oxidation errors, including 36 with medium-chain acyl-CoA dehydrogenase deficiency. Details of the methodology are presented and the potential of this screening technology is discussed.

Amino Acids↗
PubMed1989

[The effect of enriched branched chain amino acid solution on amino acid metabolism during perioperative total parenteral nutrition support].

A prospective, randomized clinical study was performed in patients underwent subtotal gastrectomy or hemicolectomy. Patients were randomly divided into two groups receiving standard amino acid solution (23% BCAA) or a solution enriched with branched chain amino acid (41% BCAA). Preoperative postprandial plasma amino acid levels were used as base line. The amino acid concentrations in plasma between control group (A) and study group (B) were compared during perioperative period. The dynamics of postoperative plasma amino acid profile of the two groups were similar except that plasma BCAA concentrations were very high in group B. In both groups, the levels of plasma glutamine, alanine, tyrosine, lysine, threonine, arginine, asparagine, and cystine decreased, whereas the levels of plasma methionine, phenylalanine, and tryptophan increased. The solution of 41% BCAA was not found to be superior to standard 23% BCAA in normalizing the disorder of plasma amino acid spectrum during the period of TPN support. The differences of urinary amino acid excretion including 3-MHIS and nitrogen balance between the two groups were not statistically significant. Also the results showed more severe disorder of plasma amino acid profile caused by 41% BCAA solution than by standard solution of 23% BCAA.

Adult↗
PubMed2004

The effect of alpha-ketoglutaric acid on amino acid utilization by nonstarter Lactobacillus spp. isolated from Cheddar cheese.

AIMS: To examine the effect of alpha-ketoglutaric acid (alpha-KG) on the utilization and catabolism of amino acids by strains of nonstarter lactobacilli isolated from Cheddar cheese. METHODS AND RESULTS: The effect of alpha-KG in the growth medium of nonstarter lactobacilli on amino acid metabolism, catabolite levels, peptide hydrolase and aminotransferase activities was examined. The pattern of amino acid utilization, catabolite formation and aminotransferase activity was affected by keto acid. CONCLUSIONS: Amino acid conversion into cheese aroma and flavour compounds by nonstarter lactobacilli is enhanced in the presence of alpha-ketoglutarate. SIGNIFICANCE AND IMPACT OF THE STUDY: Increasing the availability of alpha-ketoglutarate in cheese offers a possible method of reducing the maturation period by accelerating the rate of character compound formation from amino acids by the nonstarter lactobacilli.

Amino Acids↗
PubMed1978

The stimulating effect of fatty acids and amino acid derivatives on the labellar sugar receptor of the fleshfly.

Seven D-amino acids, including D-valine, D-phenylalanine, D-leucine, D-isoleucine, D-tryptophan, D-methionine, and D-alpha-aminobutyric acid, are markedly less stimulative than the corresponding L-isomers that can stimulate the labellar sugar receptor of the fleshfly. A distinct effect of len;th of the amino acid side chain is clearly observed. Esterification and amidation of the alpha-carboxyl group, as well as substitution by hydroxyl and methyl groups, result in extremely decreased responses. Amino acids whose amino groups are located at a position other than the alpha are almost ineffective. With all these rigid stereospecificities of the sugar receptor for amino acids, certain replacement of the alpha-amino group with the hydroxyl or carbonyl group shows a slight increase of the response at neutral pH. Furthermore, certain fatty acids can stimulate the sugar receptor once the solutions are buffered at neutral pH. This observation was further supported by the presence of a remarkable similarity of stimulating effectiveness between amino acids that can stimulate the sugar receptor and those fatty acids. The similarity was shown by testing the response concentration relationships, the stimulating effect of fatty acid derivatives, the effect of treatment with p-chloromercuribenzoate, the behavioral response, and so on.

Amino Acids↗
PubMed1980

Effects of dietary amino acids on brain amino acids and transmitter amines in rats with a portacaval shunt.

The etiologic relationship between disturbances in metabolism of amino acids and amines and hepatic coma was investigated by examining the effects of diets containing various mixtures of amino acids on brain amine metabolism in rats with a portacaval shunt, using a method for simultaneous analysis of amino acids and amines. Rats with a portacaval shunt were fed on four different amino acid compositions with increased amounts of various amino acids suspected to be etiologically related to hepatic coma, such as methionine, phenylalanine, tyrosine, and tryptophan. The animals were killed 4 weeks after operation. During the experimental period, these animals did not become comatose, but exhibited various behavioral abnormalities. Marked increase in the plasma and brain levels of the augmented amino acids, especially methionine and tyrosine, were observed in rats with a portacaval shunt. Brain noradrenaline, dopamine, and serotonin levels were significantly decreased when the brain tyrosine level was increased. These results indicate that in rats with a portacaval shunt the dietary levels of amino acids greatly influence the brain levels of both amino acids and transmitter amines.

Amino Acids↗
PubMed1994

Amino acid profile and aromatic amino acid concentration in total parenteral nutrition: effect on growth, protein metabolism and aromatic amino acid metabolism in the neonatal piglet.

1. The protein and amino acid utilization of two commercially available amino acid solutions, one egg-patterned (Vamin), the other human-milk-patterned (Vaminolact), were studied in piglets receiving total parenteral nutrition. It was hypothesized that Vaminolact was deficient in total aromatic amino acids, so a third group received a human-milk-patterned amino acid solution with added phenylalanine. 2. The piglets were on total parenteral nutrition for 8 days from day 2 or 3 of life. They all received a total energy intake of 1040 kJ day-1 kg-1 with macronutrient intakes of 14.6 g of amino acid, 27.4 g of glucose and 9.4 g of fat day-1 kg-1. 3. Nitrogen balances were performed on days 3-8 of total parenteral nutrition. On day 8 a primed constant infusion of (1-14C]-phenylalanine was given to measure phenylalanine flux and fractional conversion to tyrosine. Transamination catabolites of phenylalanine and tyrosine were measured in urine on day 7. 4. The piglets receiving Vaminolact gained significantly less weight (0.86 kg compared with 1.18 kg for Vamin and 1.20 kg for phenylalanine-supplemented Vaminolact; P < 0.02) and nitrogen (1435 mg day-1 kg-1 compared with 1601 mg and 1836 mg day-1 kg-1 for the other groups; P < 0.0001). 5. The piglets receiving Vamin had high plasma phenylalanine levels (2234 mumol/l compared with 156 mumol/l for Vaminolact and 399 mumol for phenylalanine-supplemented vaminolact; P < 0.0001). Those receiving Vamin also had an elevated excretion of phenylalanine transamination metabolites and low plasma lysine levels. Phenylalanine flux was highest in the Vamin group, intermediate in the phenylalanine-supplemented Vaminolact group and lowest in the Vaminolact group. 6. We conclude that Vaminolact is limiting in aromatic amino acids and that the addition of phenylalanine to the level in Vamin significantly improves growth and nitrogen retention; however, increasing the phenylalanine content of total parenteral nutrition is not the most metabolically suitable way to provide aromatic amino acids in neonatal total parenteral nutrition.

Amino Acids↗
PubMed1975

Transformation of some hydroxy amino acids to other amino acids.

It has been observed that beta-hydroxy-alpha-amino acids are transformed into other amino acids, when heated in dilute solutions with phosphorous acid, phosphoric acid or their ammonium salts. It has been shown that as in the case of previously reported glycine-aldehyde reactions, glycine also reacts with acetone to give beta-hydroxyvaline under prebiologically feasible conditions. It is suggested, therefore, that the formation of beta-hydroxy-alpha-amino acids and their transformation to other amino acids may have been a pathway for the synthesis of amino acids under primitive earth conditions.

Amino Acids↗
PubMed1989

Reversed-phase high-performance liquid chromatography separation of dimethylaminoazobenzene sulfonyl- and dimethylaminoazobenzene thiohydantoin-amino acid derivatives for amino acid analysis and microsequencing studies at the picomole level.

A simple and fast reversed-phase high-performance liquid chromatographic method has been developed for the complete separation of 35 dimethylaminoazobenzene sulfonyl (DABS)-amino acids and by-products. This method allows simultaneous determination of primary and secondary amino acids which can be present in protein and peptide hydrolysates and also detects the presence of cysteic acid, S-sulfocysteine, hydroxyproline, taurine, norleucine, cystine, and delta-hydroxylysine. The precolumn derivatization of amino acids with dimethylaminoazobenzene sulfonyl chloride (DABS-Cl) is simple and quick (10 min at 70 degrees C) and allows the complete reaction of primary and secondary amino acids. The separation of the compounds under investigation is achieved in 25 min using a reversed-phase 3-microns Supelcosil LC-18 column at room temperature. The versatility of the proposed method is documented by amino acid determination on protein samples obtained using different hydrolysis techniques (HCl, methane-sulfonic acid, and NaOH), with attention given to the detection of tryptophan in protein samples with high sugar concentration. Furthermore, we have reported the experimental conditions necessary to apply this method to the amino acid analysis of very low amount of proteins (1 to 5 micrograms) electroeluted from a stained band after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The stability of DABS-derivatives, the short time of analysis, the high reproducibility and sensitivity of the system, and the complete resolution of all compounds of interest make this method suitable for routine analysis. Furthermore, we have also developed a fast reversed-phase high-performance liquid chromatographic method for the complete separation of dimethylaminoazobenzene thiohydantoin (DABTH)-amino acids. The separation of the compounds under investigation is obtained, at room temperature, in less than 18 min using a reversed-phase Supelcosil LC-18 DB column, 3-micron particles, and also allows the complete separation of DABTH-Ile, DABTH-Leu, and DABTH-Norleu. The short time of analysis, together with the high reproducibility of the system and its sensitivity at picomole levels, make this method very suitable for the identification of DABTH-amino acids released during microsequencing studies of proteins and peptides with the dimethylaminoazobenzene isothiocyanate reagent. In addition, we have shown that it is possible to obtain complete separation of DABTH-amino acids also under isocratic conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗
PubMed1981

A comparison of the effects of intravenous infusion of individual branched-chain amino acids on blood amino acid levels in man.

1. Intravenous infusions of L-valine (600 mumol/min), L-isoleucine (150 mumol/min), L-leucine (300 mumol/min) and a mixture of the three branched-chain amino acids (70% L-leucine, 20% L-valine, 10% L-isoleucine; 270 mumol/min) were given to four groups of healthy volunteer subjects. Whole-blood concentrations of amino acids and glucose and serum insulin were measured before and during the infusions. 2. Valine and isoleucine infusions resulted in twelve- and six-fold increases in the respective amino acid. During valine infusion, tyrosine was the only amino acid for which a decrease in concentration was seen (25%, P less than 0.05). With isoleucine administration, no significant changes were found. In contrast, leucine infusion (during which the leucine concentration rose about sixfold) was accompanied by significant decreases in tyrosine (35%), phenylalanine (35%), methionine (50%), valine (40%) and isoleucine (55%). The arterial glucose concentration fell slightly (5%) and the insulin concentration increased 20% during leucine infusion. 3. Infusion of the mixture of the three branched-chain amino acids resulted in marked decreases in tyrosine (50%), phenylalanine (50%) and methionine (35%). The decreased amino acid levels remained low for 2 h after the end of the infusion. 4. The present findings demonstrate that intravenous infusion of leucine (not infusion of valine or isoleucine) results in marked reductions in the concentrations of the aromatic amino acids and methionine. Infusion of a mixture of the three branched-chain amino acids gives results similar to those obtained with leucine infusion alone. Thus a mixed branched-chain amino acid solution with leucine as its main constituent seems to be the best alternative in the treatment of patients with hepatic cirrhosis and encephalopathy.

Adult↗
PubMed2001

Reduction of nonpolar amino acids to amino alcohols to enhance volatility for high-precision isotopic analysis.

Amino acids are routinely derivatized using carbon-containing groups prior to gas chromatography continuous-flow isotope ratio mass spectrometry (GCC-IRMS). Derivative C contaminates analyte C because the entire derivatized compound is combusted to CO2. Correction procedures are required to extract the analyte isotope ratio. We present a method for reduction of six nonpolar amino acids to their corresponding amino alcohols, demonstrate a GC strategy to produce acceptable peak shapes from the resulting strongly H-bonding analytes, and present isotopic analysis for amino acids and their corresponding amino alcohols to evaluate any possible isotopic fractionation. Alanine, valine, leucine, isoleucine, methionine, or phenylalanine was reduced using NaBH4 in THF with I2 as an electrophile. Reactions were performed with 2 g of analyte to permit isotopic analysis by conventional elemental analysis-IRMS. All reactions were quantitative as assessed by IR spectra, melting points, and GC. Recovery from the reaction mixture was 60-84%. GC separation of a mixture of the six amino alcohols was achieved using a thick stationary-phase (5 microm) capillary column to avoid tailing due to hydrogen bonding to the walls of the fused-silica capillary. The reproducibility of GCC-IRMS determinations of amino alcohols averaged SD(613C) = 0.25 +/- 0.19%. The absolute differences between delta13C of amino acids measured by an elemental analyzer coupled to IRMS and amino alcohols measured by GCC-IRMS was delta613C = 0.14% and showed no general trend. Reactions performed with 2 mg of analyte yielded equivalent chromatograms. These data indicate that the reduction method does not induce isotopic fractionation and can be used for continuous-flow isotopic analysis to avoid addition of contaminating carbon.

Amino Acids↗
PubMed1996

Comparison of the autoradiographic binding distribution of [3H]-gabapentin with excitatory amino acid receptor and amino acid uptake site distributions in rat brain.

1. Gabapentin is a novel anticonvulsant with an unknown mechanism of action. Recent homogenate binding studies with [3H]-gabapentin have suggested a structure-activity relationship similar to that shown for the amino acid transport system responsible for the uptake of large neutral amino acids (LNAA). 2. The autoradiographic binding distribution of [3H]-gabapentin in rat brain was compared with the distributions for excitatory amino acid receptor subtypes and the uptake sites for excitatory and large neutral amino acids in consecutive rat brain sections. 3. Densitometric measurement of the autoradiographic images followed by normalisation with respect to the hippocampus CA1 stratum radiatum, was carried out before comparison of each binding distribution with that of [3H]-gabapentin by linear regression analysis. The correlation coefficients observed showed no absolute correlation was observed between the binding distributions of [3H]-gabapentin and those of the excitatory amino acid receptor subtypes. The acidic and large neutral amino acid uptake site distributions demonstrated a much closer correlation to the [3H]-gabapentin binding site distribution. The correlation coefficients for D-[3H]-aspartate, L-[3H]-leucine and L-[3H]-isoleucine binding site distributions were 0.76, 0.90 and 0.88 respectively. 4. Concentration-dependent inhibition by unlabelled gabapentin of autoradiographic binding of L-[3H]-leucine and L-[3H]-isoleucine was observed, with non-specific binding levels being reached at concentrations between 10 and 100 microM. 5. Excitotoxic quinolinic acid lesion studies in rat brain caudate putamen and autoradiography were carried out for the amino acid uptake sites mentioned above. The resulting glial infiltration of the lesioned areas was visualized by autoradiography using the peripheral benzodiazepine receptor specific ligand [3H]-PK11195. A significant decrease in binding density in the lesioned area compared with sham-operated animals was observed for D-[3H]-aspartate, L-[3H]-leucine, L-[3H]-isoleucine and [3H]-gabapentin, whilst [3H]-PK11195 showed a significant increase in binding density indicative of glial infiltration into the lesioned area. These results suggest that the gabapentin binding site and the acidic and LNAA uptake site may be present on cell bodies of a neuronal population of cells. 6. From these studies it appears that [3H]-gabapentin, L-[3H]-leucine and L-[3H]-isoleucine bind to the same site in rat brain. The inhibition of [3H]-gabapentin binding by the LNAA uptake system-specific ligand, BCH, suggests that [3H]-gabapentin may label this uptake site, termed system-L. Conversely these ligands could be labelling a novel site that coincidentally has a similar structure-activity relationship to this uptake site. These results suggest a novel mechanistically relevant site of action for gabapentin and may enable further anti-epileptic agents of this type to be developed.

Acetates↗