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PubMed1995

Determination of amino acids by on-line capillary electrophoresis-electrospray ionization mass spectrometry.

On-line capillary electrophoresis-electrospray ionization mass spectrometry (CE-ESMS) has been used for the separation and detection of amino acid mixtures. Four natural amino acids, histidine, tryptophan, phenylalanine, aspartic acid, and a tripeptide, glutathione, were separated and determined. Protonated molecules were detected in the CE-ESMS mode with detection limits of about one pmol. Optimum CE-ESMS operating conditions for amino acid analysis were determined employing acetic acid solutions as CE electrolytes. The examined parameters included capillary diameter (50-100 microns internal diameter), applied separation voltage (20-30 kV), and concentration of electrolyte (10-60% acetic acid). Stable working conditions were maintained when the CE currents were less than 18 microA. The use of electrolyte solutions such as those described here instead of true buffer solutions may have advantages for CE-ESMS systems which employ a "sheathless" interface.

Amino Acids↗

PubMed1986

Effect of amino acids on expression of K99 adherence pili by Escherichia coli.

Various common L-amino acids differed in their ability to suppress K99 production in E. coli. Strains of E. coli also varied in their sensitivity to amino acid-mediated suppression of K99. Alanine, methionine, leucine, and valine were the most suppressive amino acids. However, when compared to single amino acids, mixtures of these amino acids were frequently either less suppressive, non-suppressive, or even stimulatory for K99 expression.

Agglutination↗

PubMed1984

Rapid ion-exchange method for the determination of 3-methylhistidine in rat urine and skeletal muscle.

A method for the determination of 3-methylhistidine using an automatic amino acid analyser has been developed. A single column system with lithium buffer (pH 3.950, 0.500 mol/l lithium and 0.067 mol/l citrate) was used for elution. The standard amino acid mixture of basic amino acids and some dipeptides usually present in physiological fluids was analysed for the development of the method. 3-Methylhistidine eluted in 46.7 +/- 0.049 min and the peak area coefficient of variation for the same sample was 1.07%. As 3-methylhistidine is completely resolved from the other basic amino acids and some dipeptides (anserine and carnosine), this method is suitable for the analysis of urine and muscle extracts as well as skeletal muscle protein hydrolysates where this amino acid is present in much lower concentrations than other amino acids.

Amino Acids↗

PubMed2000

L-amino acid sensing by the extracellular Ca2+-sensing receptor.

The extracellular calcium (Ca(2+)(o))-sensing receptor (CaR) recognizes and responds to (i.e., "senses") Ca(2+)(o) as its principal physiological ligand. In the present studies, we document that the CaR is activated not only by extracellular calcium ions but also by amino acids, establishing its capacity to sense nutrients of two totally different classes. l-Amino acids, especially aromatic amino acids, including l-phenylalanine and l-tryptophan, stereoselectively mobilized Ca(2+) ions in the presence of the CaR agonists, Ca(2+)(o), gadolinium (Gd(3+)(o)), and spermine in fura-2-loaded human embryonic kidney (HEK-293) cells stably transfected with the human CaR. l-amino acid-dependent effects were observed above, but not below, a threshold level of Ca(2+)(o) of approximately 1.0 mM. l-Amino acids, particularly aromatic amino acids, also stereoselectively enhanced the sensitivity of the CaR to its agonists, Ca(2+)(o) and spermine. Branched-chain amino acids were almost inactive, and charged amino acids, including arginine and lysine, were much less effective than aromatic and other amino acids. l-amino acid mixtures emulating the amino acid composition of fasting human plasma reproduced the effects of high concentrations of individual l-amino acids on Ca(2+) mobilization and enhanced the sensitivity of the CaR to Ca(2+)(o). The data presented herein identify the CaR as a molecular target for aromatic and other l-amino acids. Thus, the CaR can integrate signals arising from distinct classes of nutrients: mineral ions and amino acids. The actions of l-amino acids on the CaR may provide explanations for several long recognized but poorly understood actions of dietary protein on calcium metabolism.

Amino Acids↗

PubMed2004

Short-term bed rest impairs amino acid-induced protein anabolism in humans.

Diminished muscular activity is associated with alterations of protein metabolism. The aim of this study was to evaluate the effect of short-term muscle inactivity on regulation of whole-body protein deposition during amino acid infusion to simulate an experimental postprandial state. We studied nine healthy young volunteers at the end of 14 day periods of strict bed rest and of controlled ambulation using a cross-over design. Subjects received a weight-maintaining diet containing 1 g protein kg(-1) day(-1). l[1-(13)C]leucine was used as a marker of whole-body protein kinetics in the postabsorptive state and during a 3 h infusion of an amino acid mixture (0.13 g amino acid (kg lean body mass)(-1) h(-1)). In the postabsorptive state, bed rest decreased (P < 0.05) the rate of leucine disposal (R(d)) to protein synthesis and tended to decrease leucine rate of appearance (R(a)) from proteolysis, whereas the rate of leucine oxidation did not change significantly. Amino acid infusion increased leucine R(d) to protein synthesis and oxidation and decreased leucine R(a) from proteolysis in both the bed rest and ambulatory conditions. Changes from basal in leucine R(d) to protein synthesis were lower (P < 0.05) during bed rest than those in the ambulatory period, whereas changes in leucine R(a) from proteolysis and oxidation were not significantly different. During amino acid infusion, net leucine deposition into body protein was 8 +/- 3% lower during bed rest than during the ambulatory phase. In conclusion, short-term bed rest leads to reduced stimulation of whole-body protein synthesis by amino acid administration. Results of this study were, in part, presented at the meeting, Experimental Biology, 2004, Washington DC.

Adult↗

PubMed2000

Poly(amino acid) bioadhesives for tissue repair.

We report here on poly(amino acid)-based bioadhesives with potential to bond to soft tissues. The systems investigated included homopolymer poly(amino acids), mixtures of poly(amino acids) and amino acids, and blends of different poly(amino acids). Adhesive performance was tested in tension on glass surfaces, chondroitin sulfate surfaces, as well as bovine cartilage surfaces. The amino acid structural units contained acidic, basic, or polar side chains and were found to adhere reasonably well to the surfaces of glass and chondroitin sulfate. The formation of polymer-monomer complexes with the addition of a basic monomer such as L-lysine to negatively charged polymers such as poly(L-aspartic acid) and poly(L-glutamic acid) was found to result in greater adhesive strength relative to homopolymers. Further improvement in adhesion was observed in blends of poly(L-lysine) with polar poly(amino acids) such as poly(L-asparagine). Adhesion on wet cartilage surfaces was the weakest measured but a priming approach designed to form electrostatic or hydrogen bonds appears promising. We believe the strength of the adhesives studied here is based on the ability of their constituent polymers and monomers to form molecular entanglements and crosslinks for load transfer. We also believe hydrogen bonds and electrostatic forces play a role in the adhesion of the systems to the substrates probed in this work.

Adhesiveness↗

PubMed1985

Feeding responses by adult males of Melanoplus sanguinipes (Fabricius) to carbohydrates and amino acids.

Adult males of Melanoplus sanguinipes (Fabricius), the migratory grasshopper, were starved for 18 h and were placed, one per arena, into arenas containing treated glass-fibre discs. The discs had been dipped into aqueous solutions of carbohydrates or amino acids of 0.0001, 0.001, 0.01, or 0.1 M concentration and allowed to dry at air temperature. They were placed vertically on pins and distributed at random among five equidistant stations around the periphery of the bottom of the arena. Each arena was provided with a glass-fibre disc that had been dipped in distilled water, as a control. The grasshoppers were allowed to feed at room temperature at 16:8 (L:D) for 24 h. Determinations of the effects of nutrient chemicals on feeding were determined by dry-weight differences between the weights of the treated discs before and after testing. Ribose, glucose, mannose and trehalose had no influence on feeding; 0.01 M fructose of 0.1 M arabinose, galactose, melibiose or sucrose increased feeding over that obtained with the control discs (P = 0.05); and 0.01 M xylose or sorbose depressed feeding. Each of the 11 amino acids investigated was phagodeterrent to adult males of M. sanguinipes. The present results confirm the variability of responses to carbohydrates among acridids; however, the reversal of phagodeterrency of sorbose or xylose at 0.1 M concentration is believed to be the first reported instance of such behaviour. In contrast to other reports of phagostimulation of acridids by individual amino acids or amino-acid mixtures, all protein amino acids tested in the present study were phagodeterrent to adult males of M. sanguinipes, even at low concentrations.

Amino Acids↗

PubMed1993

Effect of a postprandial amino acid pattern on gastric acid secretion in man.

In the present study it was the aim to examine the effect of a postprandial plasma amino acid pattern on gastric acid secretion in man. Firstly, a new amino acid mixture of 18 amino acids was administered intravenously (10 g/h) to 8 normal subjects and the plasma amino acid levels correlated well with those observed after ingestion of a protein-rich meal (r = 0.91; p < 0.001). The i.v. administration of this solution elicited a small though significant augmentation of basal acid secretion (3.1 mmol/h) compared to controls while pentagastrin-stimulated (50 ng/kg/h) gastric acid secretion remained unaffected. In addition, plasma gastrin levels remained unchanged in the basal state during i.v. infusion of the amino acid solution. These results indicate that elevations of circulating plasma amino acid levels similar to those after ingestion of a protein-rich meal have--if at all--only a small stimulatory effect on basal acid secretion. Since plasma amino acids increase when gastric acid secretion has already been activated by cephalic or gastric phase mechanisms, their physiological relevance for the regulation of gastric acid secretion is negligible.

Adult↗

PubMed1996

Studies on the inhibition of pancreatic and carboxylester lipases by protamine.

The basic protein protamine strongly inhibited hydrolysis of triolein emulsified with soybean phosphatidylcholine (PC) by pancreatic and carboxylester lipases; 10 micrograms/ml protamine, about 1000 times lower than the concentration of bovine serum albumin for the same effect, inhibited triolein hydrolysis completely. This inhibition was not affected by the incubation pH or bile salt concentration. Two other basic proteins, histone and purothionin, also inhibited hydrolysis of triolein emulsified with soybean PC, but they did not inhibit triolein hydrolysis by gastric lipase. When gum arabic was used as an emulsifier instead of soybean PC, these basic proteins did not affect triolein hydrolysis by pancreatic or carboxylester lipases. The effects of protamine on triolein hydrolysis by pancreatic and carboxylester lipases was studied using various phospholipids as emulsifiers. Protamine (10 micrograms/ml) did not inhibit hydrolysis of triolein emulsified with dicaproyl PC (DCPC), phosphatidic acid (PA), or phosphatidylserine (PS) by pancreatic and carboxylester lipases. Conversely, protamine at high concentrations slightly stimulated hydrolysis of triolein emulsified with DCPC or PA. Hydrolysis of triolein-phosphatidylethanolamine (PE) emulsion was inhibited slightly by protamine. The profiles of protamine inhibition of triolein-phosphatidyl-N,N-dimethyl ethanolamine (PDME) and triolein-phosphatidyl-N-monomethyl ethanolamine (PMME) emulsions were intermediate between those of PC and PE emulsions. These results suggest that the phospholipid species, especially choline moieties and fatty acid chain length, affect the lipase inhibitory activity of protamine profoundly. In vivo, oral administration of protamine to rats reduced and delayed the peak plasma triacylglycerol concentration, but neither bovine serum albumin nor an amino acid mixture with an amino acid composition identical to protamine affected plasma triacylglycerol levels.

Animals↗

PubMed1977

Multiple-carbon-source-limited growth kinetics of a marine coryneform bacterium.

The steady-state growth rate of a marine isolate was related to the concentrations of several carbon and energy source substrates when these substrates limited growth simultaneously in continuous culture. Glucose limitation was characterized by a threshold of 0.21 mg/liter for growth, a half-maximal growth rate at 0.48 mg/liter, U-shaped curves in extractable pool concentration-versus-growth velocity plots, and slow maximal growth rates. Arginine addition reduced the glucose threshold to 0.008 mg/liter, more than doubled the maximal growth rate, and stabilized pool concentrations at low growth rates. Addition of a third substrate, glutamate, caused further reduction of the glucose concentration a steady state. Maximal reduction of the glucose concentration was effected by adding a mixture of 20 amino acids. Steady-state limiting nutrient concentration was dependent on the specific identity of the auxiliary nutrients and on the concentration ratio at which they were supplied. When glucose was supplemented with an equal quantity of an amino acid mixture, the external steady-state glucose remained below 10 mug/liter. When 1 mug of glucose was added to a 2.5-mg/liter amino acid mixture, at least 70% of it was consumed at steady state in spite of the threshold observed. Lack of crossover between metabolic pathways, suggested by the absence of glucose carbon in pool glutamate of arginine-glucose-grown cells, may have been partly responsible for the mixed carbon source stimulation of nutrient accumulation observed. The affinity observed is sufficient to account for normal growth at a total organic substrate concentration of only 0.11 mg/liter when supplied from a suitable mixture.

Amino Acids↗

PubMed1982

Effects of amino acids and gastric inhibitory polypeptide on insulin release in dogs.

Insulin release following intravenous administration of an amino acid solution with and without a simultaneous infusion of varying amounts of porcine gastric inhibitory polypeptide (GIP) was studied in dogs. Group I received a 10-amino acid mixture (300 mosmol/kg iv) at 16.6 ml/min for 1 h; group II, amino acid mixture plus 0.5 micrograms.kg-1.h-1 porcine GIP; group III, amino acid mixture plus 1.0 micrograms.kg-1.h-1 of GIP; group IV (a and b) received either 0.5 or 1.0 micrograms.kg-1.h-1 of GIP alone. Compared to group I, groups II and III had a greater insulin response during the first 30 min of the infusion. Group] IV (a and b) showed no insulin release. Glucose concentrations showed no significant change in all groups. From these results, it is concluded that insulin release after intravenous infusion of an amino acid mixture plus GIP is greater than after amino acids or GIP alone. It appears that this effect is more pronounced in the early phase of insulin release.

Amino Acids↗

PubMed2003

Fos immunocytochemical studies on the neuroanatomical sites of action of acute tyrosine depletion in the rat brain.

RATIONALE: Acute depletion of brain tyrosine using a tyrosine-free amino acid mixture offers a nutritional approach to reduce central catecholamine function. Recent preclinical data suggest that tyrosine-free amino acid mixtures may have region-specific effects through targeting dopamine neurones. OBJECTIVES: Here we used fos immunocytochemistry to examine the neuroanatomical sites of action of a tyrosine-free amino acid mixture administered either alone or combined with amphetamine. METHODS: Rats (male, Sprague Dawley, 240-260 g) were administered (IP) either a tyrosine-free amino acid mixture (1 g/kg), or the same mixture supplemented with tyrosine and phenylalanine (1 g/kg). Mixtures were injected twice (1 h apart) followed 1 h later by amphetamine (2 mg/kg SC). Two hours later, cardiac perfusion was performed and brains were processed for fos immunocytochemistry. Fos positive cells were counted using computer imaging software. RESULTS: The tyrosine-free amino acid mixture alone did not alter fos expression in ten regions of the rat forebrain compared to saline controls. However, the mixture reduced the increase in fos expression evoked by amphetamine. This effect was region-specific and was greatest in caudate putamen, nucleus accumbens, bed nucleus stria terminalis and lateral habenula, and lacking in other areas including cingulate and insular cortices, lateral septum and central amygdaloid nucleus. Moreover, in most regions the effect of the tyrosine-free mixture was less after tyrosine and phenylalanine supplementation. CONCLUSIONS: In summary, a tyrosine-free amino acid mixture reduced amphetamine-induced fos expression but this effect was region-specific and included dopamine-rich regions. These data further support the idea that tyrosine depletion strategies have potential as treatments for mania and other hyperdopaminergic states.

Amphetamine↗

PubMed1979

Protein amino acid analysis by an isotope ratio gas chromatography mass spectrometry computer technique.

A method for quantitative analysis of protein amino acids by a gas chromatography mass spectrometry computer system is described. Amino acids were analysed as their N-trifluoroacetyl n-butyl ester derivatives. Isotope ratio determination was used as the quantitating technique via multiple internal standards. The exact composition of a deuterated amino acid mixture was determined against a standard amino acid calibration mixture and in turn the protein amino acid composition was determined against the deuterated amino acid mixture. The amount of protein taken for analysis was 100 micrograms and the procedure, excluding hydrolysis, could be performed with 2 1/2 hours. The introduction of the internal standards prior to protein hydrolysis provides a method with good precision (mean coefficient of variation less than 5%). The method, tested on insulin, gave results which agreed well with the known composition of the protein and with simultaneous analysis on ion exchangers.

Amino Acids↗

PubMedDate not supplied

Anticatabolic effect of branched-chain amino acid-enriched solutions in patients with liver cirrhosis.

An amino acid mixture rich in branched-chain amino acids and poor in aromatic amino acids was infused in six cirrhotics with altered plasma amino acid profile and normal mental state. The effect on muscle protein catabolism, as measured by urinary excretion of 3-methylhistidine, was assessed during two consecutive 3-day period in which patients received the amino acid mixture alone or in a hypertonic dextrose solution. During a 3-day basal period, cirrhotics showed increased rates of 3-methylhistidine excretion as compared to six matched healthy subjects. Both treatments reduced urinary 3-methylhistidine to normal. During treatment, branched-chain amino acids failed to normalize, plasma aromatic amino acid concentrations and ammonia declined, and alanine increased. Branched-chain amino acids are mainly oxidized in skeletal muscle with production of alanine. Reduced muscle protein catabolism following amino acid infusion is consistent with the physiological role of branched-chain amino acids in suppressing protein breakdown and stimulating protein synthesis. Long-term therapy with branched-chain amino acid-enriched mixtures may prove useful in advanced cirrhotics with severe muscle wasting.

Adult↗

PubMed1984

The effect of amino acid excess on utilization by the rat of the limiting amino acid--threonine.

A threonine-deficient amino acid mixture was developed by decreasing the level of threonine in a well-balanced amino acid mixture while measuring the response in daily gain and protein retention in young growing rats. The diet that contained the highest level of threonine and yet permitted further responses in growth and protein retention was used to define a threonine-deficient amino acid mixture. This mixture was used to provide three dietary levels of threonine (0.38, 0.43 or 0.48%) in combination with three levels of relative excess of all other amino acids (0, 25 or 50% relative excess). Food intake, weight gain and changes in carcass composition were measured in the 21-day study. When voluntary food intake is used as a covariate in the analysis of these data, the level of the threonine-deficient amino acid mixture is positively correlated with body weight, dry matter, crude protein and ash gains and negatively associated with lipid deposition. However, there were no significant effects of amino acid excess on any of the responses when differences in voluntary food intake are accounted for in the statistical analysis. These data demonstrate that some aspects of threonine imbalance (food intake and lipid deposition) are dependent on the dietary level of threonine. The major effects of threonine imbalance are due to decreased voluntary food intake rather than changes in the efficiency of use of ingested threonine.

Amino Acids↗

PubMed1975

Future trends in parenteral nutrition.

With our present knowledge of total, intravenous nutrition it is now possible to eliminate, or greatly reduce, the incidence of malnutrition, as a complication of various medical and surgical conditions in modern hospitals. There is a tendency to include supplementary or total intravenous nutrition in the feeding program of the hospital, to ensure that the patients get an adequate daily amount of nutrients. The trend in the development of intravenous nutrition is, to supply all nutrients in the same proportions as those in which they enter the general circulation following a well-balanced oral food intake. Various mixtures of amino acids have been used as part of a complete intravenous nutrition. All studies in this field indicate a trend to use those amino acids mixtures which contain the essential and the nonessential L-amino acids in the same proportions as are found in the aminogram of proteins with high biological value. There is a trend to include fat, as fat emulsion (soybean oil-egg yolk-phospholipid emulsion), for intravenous nutrition, in an amount corresponding to about 40 energy percent as both the source of energy and of essential fatty acids for the body. To make an intravenous nutrition as complete as possible, all essential minerals should be included. Phosphorus is of special interest here as it aids in the prevention of hypophatemia and tissue anoxia caused by deficiency of diphosphateglycerate in the erythrocytes. Zinc may also be mentioned because of its importance for wound healing. There is also a tendency to include all the 13 necessary vitamins in an intravenous feeding program. In this connection vitamin K1 is of special importance. If patients on intravenous nutrition are treated with antibiotics, this may result in a change in the intestinal flora and a loss of intestinal vitamin K production, causing vitamin K deficiency, with severe or fatal bleeding. Consequently, vitamin K1 should be given daily to every patient on intravenous alimentation. The future trend in parenteral nutrition will also be to use this method for exact nutrition balances. In this way it will be possible to determine the endogenous loss via feces, as well as to study the requirements of nutrients in different conditions.

Amino Acids↗

PubMed1985

Absorption and retention of selenium from intrinsically labeled egg and selenite as determined by stable isotope studies in humans.

A study was carried out with four healthy young adult men, consuming a self-selected diet, to investigate quantitative aspects of the gastrointestinal absorption, urinary excretion, and body retention of egg selenium in comparison with selenite. The approach involved simultaneous consumption of egg biologically labeled (intrinsic) with the stable isotope 74Se and a dose of selenite labeled with 76Se (extrinsic label). Four labeled test diets, given on days 6, 16, 26, and 36 of the study were employed, each differing in their protein source: test diet I, 74Se-labeled egg white; diet II, 74Se-labeled egg yolk (high labeling dose) plus balanced L-amino acid mixture; diet III, 74Se-labeled egg yolk (low labeling dose) plus balanced amino acid mixture; and diet IV, balanced amino acid mixture extrinsically labeled with both 74SeO32- and 76SeO32-. The latter diet was included to assess the magnitude of any cross-isotope methodological bias. Fractional absorption (means +/- SEM) for Diet IV was 0.771 +/- 0.010 for the 74SeO32- and 0.656 +/- 0.021 for the 76SeO32- (ratio: 0.851 +/- 0.020); reflecting a small overall cross-isotope bias. Accepting the measurements made with 74SeO32- as the more accurate, experimentally determined values of absorption for the extrinsic tag were adjusted accordingly. The corrected absorption for these diets (% of dose) was (mean +/- SEM; first value for intrinsic label, second value for extrinsic label): diet I, 54.1 +/- 0.7 and 55.4 +/- 2.2; diet II, 76.7 +/- 0.8 and 83.0 +/- 1.8; diet III, 79.0 +/- 1.5 and 85.2 +/- 4.0.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1981

Histidine deficiency, food intake and growth in normal and Walker 256 carcinosarcoma-bearing rats.

Male Sprague-Dawley rats with and without growing Walker 256 tumors were fed 3 isonitrogenous, isoenergetic, semisynthetic diets. The N sources of the 3 diets were casein, a complete free amino acid mixture simulating casein, and the same amino acid mixture but now totally lacking histidine. Tumor-free rats and host and tumor components of tumor-bearing rats showed identical growth on the casein and on the casein-simulating free amino acid diets. Change from complete amino acid diet to histidine-free diet depressed food intake identically in controls and tumor-bearers in early stages of tumor growth. In later stages of tumor growth, when tumor-induced hypophagia had become apparent on the complete diet, the histidine-free diet had a progressively less depressive effect on food intake in the tumor-bearers.

Aging↗