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At least 487 records · Page 27Linked to original sources
PubMed1992

Reversed-phase chromatography of phenylthiocarbamyl amino acid derivatives of physiological amino acids: an evaluation and a comparison with analysis by ion-exchange chromatography.

Reversed-phase chromatography of phenylthiocarbamyl (PTC) amino acid derivatives of physiological amino acids was evaluated and compared with the traditional method of ion exchange. The PTC amino acid derivatives were stable for at least 32 h at ambient temperature before injection. The relationship of detector response to concentration for the PTC derivatives was linear from 39 to 1250 pmol. With few exceptions, the within- and between-run precisions of plasma amino acid retention times were less than 0.2 and 0.3%, respectively; the within- and between-run precisions of their concentrations were less than 4.0 and 5.0%, respectively. Twenty-four plasma samples were quantitated by both reversed-phase and ion-exchange chromatography; fifteen of the twenty amino acids determined had correlation coefficients in the range 0.81-1.00. Nine non-standard amino acids and ten therapeutic drugs were added to plasma; D-glucosaminic acid and alpha-amino-beta-guanidinopropionic acid co-eluted with alpha-aminoadipic acid and threonine, respectively. Of the ten drugs added, only metronidazole and theophylline co-eluted with beta-alanine and histidine, respectively. The precision, stability, and sensitivity of the method render it ideal for the quantitation of plasma amino acids.

Amino Acids↗
PubMed1999

An intragastric amino acid mixture influences extracellular amino acid profiles in the lateral hypothalamic area of freely moving rats.

We tested the effect of equicaloric loads of glucose (0.89 g) or a balanced amino acid mixture (0.85 g) on extracellular amino acid concentrations in the brains of freely moving rats. At 15:30 hours, the microdialysis probe was inserted into the lateral hypothalamic area of ambulatory rats, and food and water were removed. Dialysates were collected every 20 min from 1 h prior to gavage (18:00 hours) and until 3 h after the gavage. Amino acid concentrations in the dialysate were determined by reverse-phase HPLC. Following the amino acid gavage, extracellular amino acid concentrations significantly increased from baseline for alanine, isoleucine, leucine, methionine, threonine, tyrosine, and valine. Those elevations occurred within 20-40 min following the amino acid load, and lasted up to 100 min. After the glucose and water treatments, amino acid concentrations were either not affected or gradually diminished from baseline. We conclude that extracellular amino acid concentration in the lateral hypothalamus is influenced by the composition of food consumed.

Administration, Oral↗
PubMed1982

[Effect of solutions with different amounts of branched-chain amino acids on the plasma amino acid pattern and energy metabolism of surgical intensive care patients].

30 intensive care surgical patients were investigated over a period of five days following trauma or major surgery. The patients were randomized into two groups. Both collectives received equal amounts of protein (1.0 g amino acids . kg-1 . d-1) and carbohydrate (6,7 g . kg-1 . d-1). Under this infusion regimen the patients of group I received an amino acid solution containing 45% branched-chain amino acids (BCCA), the patients of group II an amino acid solution with a 10% content of BCAAs. After only 24 hrs of infusion, the total amino acid concentration and branched-chain amino acid concentration in the plasma of patients receiving the solutions containing 45% BCAAs already clearly exceeded reference range, and continued increase during the entire investigation period. In those patients receiving the 10% branched-chain amino acid solution, these parameters rapidly returned to normal and then remained within reference range. Cumulative nitrogen balance and nitrogen balance on each day of investigation were significantly less negative in those patients administered the amino acid solution with small amounts of BCAAs. These results seem to indicate that after severe trauma or major surgery amino acid solutions containing high concentrations of BCAAs may be an unphysiological load on the already stressed metabolism, rather than a benefit

Adult↗
PubMed1992

Activating regions of yeast transcription factors must have both acidic and hydrophobic amino acids.

Two similarities among transcriptional activating regions of many eukaryotic transcription factors, like those from GAL4, GCN4, and VP16, are that they have a net negative charge, and that many of them can potentially form amphipathic alpha-helices with acidic amino acids on the hydrophilic face. Based on these similarities, E. Giniger and M. Ptashne previously designed a short peptide (AH) which is predicted to have the potential to form a negatively charged amphipathic alpha-helix; AH was able to mediate transcription activation in yeast when it was attached to the DNA binding and dimerization portion of GAL4 [GAL4(1-147)]. This paper describes screening of a pool of AH derivatives containing randomized amino acids fused to GAL4(1-147) and to an analogous region of LexA [LexA(1-87)] in yeast strains. Results suggest that both acidic and hydrophobic amino acids are critical features of activating regions--these results are consistent with the model that activating regions often form amphipathic alpha-helices. This work is novel because hydrophobic amino acids are also shown to be important in activating regions of yeast transcription factors.

Amino Acid Sequence↗
PubMed1998

Epidermal growth factor (EGF) increases the renal amino acid transport capacity in amino acid loaded rats.

In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal amino acid handling was investigated in glutamine, arginine (both 50 mg/100 g b.wt. per hour), or alanine (90 mg/100 g b.wt. per hour) loaded animals. Continuous infusions of the three amino acids were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment (8 micrograms/100 g b.wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was followed by a stimulation of renal amino acid reabsorption. The increase in the fractional excretion of the administered amino acids was significantly lower than in non-EGF-treated rats. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pretreatment (0.96 +/- 0.10 vs. 0.62 +/- 0.07 ml/min x 100 g b.wt.) and a distinct increase in sodium excretion (2.98 +/- 0.55 vs. 4.97 +/- 0.71 muval/100 g b.wt. x 20 min). After loading with p-aminohippurate (PAH; 200 mg/100 g b.wt.), PAH excretion in EGF rats was increased by about 20%, whereas urinary protein excretion was lower in EGF pretreated rats (control: 0.45 +/- 0.04 vs. EGF: 0.18 +/- 0.03 mg/100 g b.wt. x 20 min). The PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions. Furthermore, EGF pretreatment depressed normal kidney weight gain significantly (874 +/- 18 vs. 775 +/- 32 mg/100 g b.wt.). EGF can improve the renal tubular transport capacity, but, compared to well-known stimulators of renal transport like dexamethasone or triiodothyronine, its effect is only of a moderate degree.

Alanine↗
PubMed1982

Prediction of plasma amino acid concentration from diet amino acid content.

The level of each plasma amino acid in male weanling rats was examined in relation to their intake from gluten, casein, synthetic amino acid, or zein diets. Plasma levels of valine, leucine, and isoleucine were found to be linearly related to the intake per gram diet regardless of the dietary source. Although levels of most other amino acids were not linearly related to intake, they were predictable if both the concentration of the amino acid in the diet and chronic level of protein intake were known. That is, a relationship, which applied to all diets, was found between the concentration of amino acid in the plasma, the concentration in the diet, and the total protein or amino acid nitrogen in the diet.

Amino Acids↗
PubMed2006

Dietary deficiencies of single amino acids: whole-body amino acid composition of adult rats.

To ascertain whether chronic amino acid deficiency alters the amino acid composition of the body, 44 adult female rats were randomly allocated to one of 11 treatments which included one control group, ingesting an adequate diet with balanced protein, and ten deficient groups in which one group received protein-deficient diets and the other groups consumed diets each deficient in a single essential amino acid. The degree of deficiency was adjusted to achieve a gradual decline in body weight to 85% of the initial weight and was then adjusted so that this weight was maintained until the end of the experiment at 93 days, when the rats were killed. Deficient rats had lower absolute weights of liver, gastrointestinal tract and muscle than animals given the adequate diet but greater relative weights (% of body weight) of heart and kidneys. There were no significant differences amongst groups in percentages of lipid, nitrogen, protein plus lipid or dry matter. Chronic marginal amino acid deficiencies did not selectively alter amino acid composition.

Amino Acids, Essential↗
PubMed2003

Weak organic acid stress inhibits aromatic amino acid uptake by yeast, causing a strong influence of amino acid auxotrophies on the phenotypes of membrane transporter mutants.

The ability of yeasts to grow in the presence of weak organic acid preservatives is an important cause of food spoilage. Many of the determinants of acetate resistance in Saccharomyces cerevisiae differ from the determinants of resistance to the more lipophilic sorbate and benzoate. Interestingly, we show in this study that hypersensitivity to both acetate and sorbate results when the cells have auxotrophic requirements for aromatic amino acids. In tryptophan biosynthetic pathway mutants, this weak acid hypersensitivity is suppressed by supplementing the medium with high levels of tryptophan or, in the case of sorbate sensitivity, by overexpressing the Tat2p high affinity tryptophan permease. Weak acid stress therefore inhibits uptake of aromatic amino acids from the medium. This allows auxotrophic requirements for these amino acids to strongly influence the resistance phenotypes of mutant strains. This property must be taken into consideration when using these phenotypes to attribute functional assignments to genes. We show that the acetate sensitivity phenotype previously ascribed to yeast mutants lacking the Pdr12p and Azr1p plasma membrane transporters is an artefact arising from the use of trp1 mutant strains. These transporters do not confer resistance to high acetate levels and, in prototrophs, their presence is actually detrimental for this resistance.

ATP-Binding Cassette Transporters↗
PubMed1985

The effect of insulin deficiency, dietary protein intake, and plasma amino acid concentrations on brain amino acid levels in rats.

The effect of diabetes (streptozotocin, 65 mg/kg ip), dietary protein intake (15-60%), and plasma amino acid concentrations on brain large neutral amino acid levels in rats was examined. After 20 days, the plasma concentrations of methionine and the branched chain amino acids (BCAA), valine, isoleucine, and leucine were increased in diabetic rats. In brain tissue, methionine and valine levels were increased but threonine, tyrosine, and tryptophan concentrations were depressed. Increased protein consumption promoted a diabetic-like plasma amino acid pattern in normal rats while enhancing that of diabetic animals. However, with the exception of threonine, glycine, valine, and tyrosine, there was little effect on brain amino acid levels. A good association was found between the calculated brain influx rate and the actual brain concentration of threonine, methionine, tyrosine, and tryptophan in diabetic animals. There was no correlation, however, between brain influx rate and brain BCAA levels. Thus, the brain amino acid pattern in diabetes represents the combined effects of insulin insufficiency and composition of the diet ingested on plasma amino acid levels as well as metabolic adaptation within the brain itself.

Amino Acids↗
PubMed2000

Chlamydial development is adversely affected by minor changes in amino acid supply, blood plasma amino acid levels, and glucose deprivation.

This study has demonstrated the extreme sensitivity of Chlamydia trachomatis growing in McCoy cells to small changes in external amino acid supply. In the absence of cycloheximide, a decrease in the amino acid concentration of medium to 75% of control values was sufficient to induce the growth of enlarged chlamydial forms of reduced infectivity. Morphology became more distorted and the yield of infectious particles from inclusions declined as medium amino acid levels were further reduced. These events correlated with a general decline in intracellular amino acids, as measured by high-performance liquid chromatography, suggesting that chlamydiae require a minimum concentration of each amino acid for normal development. Cycloheximide enhanced the production of normal organisms and increased infectivity yield in media, suggesting that the drug increased the available pool of amino acids. This was supported by intracellular amino acid analyses. Aberrant forms with reduced infectivity were also induced during supply of infected cell cultures with medium containing blood plasma amino acid concentrations, supporting the proposal that nutrient levels in vivo could promote abnormal chlamydial development. Markedly abnormal forms were also observed during glucose deprivation, providing further evidence that aberrant development is a general stress-related response.

Amino Acids↗
PubMed2000

Comparison of amino acid sequences at the amino acid 130-160 region of VP1 polypeptide of Indian field isolates of foot-and-mouth disease virus serotype Asia 1.

The nucleotide and deduced amino acid sequences in the amino acid (aa) 130-160 region of VP1 polypeptide of 65 field isolates of foot- and mouth disease virus (FMDV) serotype Asia 1 were determined and the consensus sequences were deduced. Comparison of amino acid sequences revealed conservation of NGK (130-132), TYG (134-136), RGD (142-144), and LPTSF (156-160) motifs and aa 148 (L) while variation was observed at the rest of the region (variability index (VI) of 2.06 to 16.85). Synonymous and non-synonymous mutations at the nucleotide level were well correlated with those of the corresponding amino acids. Comparison of the aa 130-160 sequence of Asia 1 serotype with those of other serotypes of FMDV revealed conservation of aa 135, 148-149, 157 and 160. Amino acids 133-138 and 148-154 were unique for Asia 1 serotype and are presumably responsible for its distinct antigenic nature. The present study revealed that the FMDV isolates of serotype Asia 1 causing outbreaks in India are very much heterogeneous in the aa 130-160 region of VP1.

Amino Acid Motifs↗
PubMed1969

Na plus-facilitated reactions of neutral amino acids with a cationic amino acid transport system.

The predominant basis for transport interactions between neutral and cationic amino acids in the Ehrlich ascites-tumor cell and the rabbit reticulocyte has been identified as a reaction of the neutral amino acid plus Na(+) with the cationic amino acid transport system. This reaction is revealed both by a Na(+)-dependent transport inhibition by the neutral amino acid, and by mutual flux accelerations whereby the neutral amino acid and Na(+) exchange for the cationic amino acid.

Amino Acids↗
PubMed1982

Crystalline amino acid diet for determining amino acid requirements of growing guinea pigs.

Crystalline amino acid diets containing different levels of total nitrogen (TN) and essential amino acid (EAA) nitrogen were evaluated in 3-week growth trials to identify a diet for use in determining the amino acid requirements of growing guinea pigs. Four levels of TN (2.5, 2.9, 3.6, and 4.3%) with constant EAA/TN ratios were compared by measuring weight gain, hemoglobin and hematocrit, carcass weight and nitrogen retention of 3-to 6-week-old male Hartley guinea pigs. Three levels of EAA nitrogen (1.7, 2.0, 2.4%), with TN levels constant at 3.6%, were also compared. A diet containing 30% casein + 0.3% arginine served as a purified control diet. Water and diets were provided ad libitum. The results of this study indicate that a diet containing 3.6% TN and 1.7% EAA nitrogen supported performance comparable to that of animals fed the casein diet. Growth rates for this amino acid diet and the casein diet both averaged 5.8 g/day.

Amino Acids↗
PubMed1998

Rat D-amino-acid oxidase cDNA: rat D-amino-acid oxidase as an intermediate form between mouse and other mammalian D-amino-acid oxidases.

Nucleotide sequence of cDNA encoding rat D-amino-acid oxidase (DAO) was determined. Two species of DAO mRNA were present in rat kidney, liver, and brain. They were probably produced by alternative splicing. Rat DAO cDNA encodes 346 amino acid residues, indicating that rat DAO is an intermediate form between mouse DAO (345 amino acids) and DAOs (347 amino acids) of human, rabbit, and pig. Deduced amino acid sequence indicates 93% identity between rat and mouse DAO. Northern hybridization and western blotting supported the sequence data.

Amino Acid Sequence↗