[Conductometric titration of amino acid or protein mixtures].
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Amino Acids↗
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Plasma amino acid analysis by isotope ratio gas chromatography mass spectrometry computer techniques.
A routine analysis for micro samples of plasma amino acids by a gas chromatography mass spectrometry computer system has been developed. Isotope ratio determination was used as the quantitating technique via multiple internal standards. The speed of the analysis is increased by omitting the ion exchange purification step and its flexibility is maximized by using repetitive scanning rather than selective ion monitoring. This procedure yields excellent precision and accuracy, as demonstrated by the analysis of a known amino acid mixture and of neonatal plasma.
Amino Acids↗
Free amino acids in crocodilians fed proteins of different biological value.
Changes in plasma levels of amino acids derived from fed protein were determined by feeding crocodilians (Caiman crocodilus crocodilus and Alligator mississipiensis) 7.5 g protein/kg body weight and by monitoring the plasma free amino acids for several days. Zein and several other vegetable proteins produced no rise in plasma amino acids and were excreted intact in the feces. Casein and fish muscle were rapidly digested but produced little rise in plasma amino acids, and the increases showed no relationship to the composition of the protein fed. Gelatin feeding led to large increases in plasma amino acids that persisted for more than a week, and the resulting pattern was nearly identical to the composition of gelatin with the exception of aspartic and glutamic acids, and several animals died. Equivalent quantities of fish muscle protein were assimilated without difficulty by the crocodilians. Endogenous protein secreted into the gut apparently contributed little to the amino acid mixture absorbed.
Alligators and Crocodiles↗
Metabolic responses to severe perinatal asphyxia in term newborn infants with particular reference to the changes in plasma free amino acids.
Blood glucose, blood lactate, plasma FFA, plasma alpha-amino nitrogen and 17 individual amino acids were determined on admission, and at 24 and 48 h after admission in severely asphyxiated term newborn infants. The blood glucose value was widely scatterred and the plasma FFA level was low on admission. The total free plasma amino acid content correlated closely with the severity of asphyxia-induced lactic acidosis. Among the 17 amino acids determined, 11 turned out to be significantly increased. The increase of plasma free amino acids might be toxic for the central nervous system, therefore parenteral feeding of asphyxiated neonates with amino acid mixtures can be dangerous.
Acidosis↗
[Future perspectives in parenteral nutrition].
Some of the future perspectives of parenteral nutrition will most likely be related to the possibilities of improving the infusion solutions used. There are studies indicating that intravenous amino acid mixtures may produce better biochemical and clinical effects either by increasing the content of histidin, arginine, tyrosine, cysteine/cystine and branched chain amino acids or by adding glutamine, ornithin, ornithin-ketoglutaric acid, taurine and glutathion. Several possibilities of improving the intravenous fat emulsions have been studied and discussed. The use of medium chain fatty acid glycerides (MCT) instead of long chain fatty acid glycerides (LCT) may be of some value. Physical mixtures of LCT and MCT have been studied. Glycerides of both medium chain and long chain fatty acids of the same glycerol molecule ('structured lipids') have also been investigated. The omega-3-fatty acids (alfalinolenic, eicosapentaenoic and docosahexaenoic acid) have unique biochemical properties which may be beneficial in various clinical situations when parenteral nutrition is indicated. Intravenous fat emulsions containing triglycerides of these fatty acids are now being extensively investigated. The omega-3-fatty acids will change the pattern of eicosanoids formed, reduce the tendency to platelet aggregation, increase the resistance to endotoxins, and reduce the viscosity of the blood. Triglycerides of gamma linolenic acid have been considered to be of value in situations when there may be a reduced activity of delta-6-desaturase to transform linoleic acid to arachidonic acid. Many other known (carnitine, non-protein sources, vitamins and trace elements) or unknown nutrients may be found to be useful in order to improve the infusion solutions used in parenteral nutrition.(ABSTRACT TRUNCATED AT 250 WORDS)
Amino Acids↗
On the abiotic formation of amino acids. I. HCN as a precursor of amino acids detected in extracts of lunar samples. II. Formation of HCN and amino acids from simulated mixtures of gases released from lunar samples.
Two studies on the abiotic formation of amino acids are presented. The first study demonstrates the role of hydrogen cyanide as a precursor of amino acids detected in extracts of lunar samples. The formation of several amino acids, including glycine, alanine, aspartic acid, and glutamic acid, under conditions similar to those used for the analysis of lunar samples is demonstrated. The second study investigates the formation of hydrogen cyanide as well as amino acids from lunar-sample gas mixtures under electrical discharge conditions. These results extend the possibility of synthesis of amino acids to planetary bodies with primordial atmospheres less reducing than a mixture of methane, ammonia, hydrogen and water.
Amino Acids↗
Post-transcriptional regulation of cysteine dioxygenase in rat liver.
Changes in hepatic cysteine dioxygenase (CDO) activity in response to diet play a dominant role in regulation of cysteine catabolism and taurine synthesis. We have conducted several studies of the molecular regulation of CDO activity in rat liver and rat hepatocytes. Compared to levels observed in liver of rats fed a basal 10% casein diet, up to 180-fold higher levels of CDO activity and protein were observed in liver of rats fed diets that contained additional protein, complete amino acid mixture, methionine, or cystine. Neither CDO activity nor CDO protein was induced by excess non-sulfur amino acids alone. Excess sulfur amino acids or protein did not significantly increase the concentration of hepatic CDO mRNA. Preliminary studies indicate that the polysome profile for association of CDO mRNA with polysomes is not altered by an increase in dietary protein level, suggesting that regulation may be posttranslational and possibly involve a decrease in the rate of CDO degradation. In primary cultures of rat hepatocytes, CDO mRNA, protein, and activity all virtually disappeared by 12 to 24 h of culture in standard medium whereas CDO protein, but not CDO mRNA, accumulated markedly between 12 and 24 h in hepatocytes cultured in medium with excess methionine or cyst(e)ine. These observations are also consistent with a limited role of transcriptional or translational regulation of CDO in response to diet.
Amino Acids, Sulfur↗
Improvement of body weight and nitrogen balance of chicks fed histidine-free or lysine-free diets with supplementation of graded levels of sulfur-containing amino acids.
To demonstrate the nutritional specificity of essential amino acids, body weight change and nitrogen balance were compared in chicks equalized-fed a histidine-free or lysine-free diet with 0, 20, 40, 60, 80, or 100% requirement of sulfur-containing amino acids (SAA). With an increase of SAA level up to 40% of its requirement, body weight and nitrogen balance increased irrespective of complete deficiency of histidine or lysine. Above 40% of the SAA requirement, these parameters reached plateaus. The intersection points of the two regression lines at which the responses of body weight change and nitrogen balance altered were 49.8 and 52.1% in the chicks fed the histidine-free diet and 44.7 and 32.6% in the chicks fed the lysine-free diet, respectively. These values are quite agreeable with the estimate of the nutritional score of the amino acid mixtures in an earlier report (Kino and Okumura, 1986). It was demonstrated that the effect of essential amino acid deficiency does not always directly associate with the percentage deficit relative to its requirement, and there exists nutritional specificity of essential amino acids.
Amino Acids, Sulfur↗
Studies on gluconeogenesis and protein synthesis in isolated hepatocytes.
Glucose production was studied in isolated hepatocytes using various substrates and with increasing substrate concentrations (0-10 mM). Fructose was the best gluconeogenic substrate while other substrates studied stimulated net glucose production in the following decreasing order: lactate, pyruvate, glycerol, galactose, alanine, and succinate. Studies on oxygen consumption showed that endogenous respiration was linear for 60 min and was not altered by extracellular calcium. Studies on the incorporation of 14C-leucine into protein was linear for only 3-4 hr in cells containing low glycogen. However, cells containing high glycogen incorporated 14C-leucine into protein linearly for 8-10 hr. About 3 mg of protein per g per hr was synthesized by isolated cells when incubated for 4 hr with amino acids mixture, glucose, lactate, and insulin.
Alanine↗
Quantitation of fourteen urinary alpha-amino acids using isobutane gas chromatography chemical ionization mass spectrometry with 13C amino acids as internal standards.
Isobutane chemical ionization gas chromatography mass spectometry of the N-trifluoroacetyl-carboxy-n-butyl ester derivatives of amino acids, using a commercial per-13C-amino acid mixture as internal standards, provided a sensitive and specific method for quantitative analysis of fourteen urinary alpha-amino acids. A computer controlled quadrupole mass spectrometer was used in a selected ion monitoring mode to record the ion current due to the protonated molecular ions of each alpha-amino acid/13C analogue pair. BASIC programmes located peak maxima, and using previously established standard curves, calculated the amino acid content on the bases of both peak height and peak area ratios. Duplicate amino acid analyses are possible on 5 microliter of urine. Instrumental analysis required 25 minutes, automated data processing 10 minutes, and sample preparation 2 hours. Detection limits approached 1 ng with a typical mean standard deviation of 2% for the instrumental analysis.
Amino Acids↗
Effect of medroxyprogesterone acetate on the efficiency of an oral protein-rich nutritional support in HIV-infected patients.
We have examined the effect of a medroxyprogesterone therapy in HIV-infected patients under appropriate nutrition for anabolism. The experiments were performed on 12 men (mean age 40 y), HIV seropositive but free of any clinically active opportunistic infection for at least one month. The patients underwent a 2-week baseline diet period (1.2 g protein x kg(-1) body weight (BW) x d(-1)) and then a 5-week experimental period with again the baseline diet in conjunction with supplements including Tonexis HP (0.7 g protein x kg(-1) BW) x d(-1)), L-threonine (0.018 g x kg(-1) BW x d(-1)) and L-methionine (0.013 g x kg(-1) BW x d(-1)). Indeed HIV-infected patients showed deficiencies in these amino acids. They were randomly divided into groups I and II under double-blinded condition. Group II was given medroxyprogesterone acetate (0.4 g x d(-1)) during the last 3 weeks whereas group I received a placebo. All the patients significantly increased their body weight (P < 0.05) during the experimental periods. Those under medroxyprogesterone tended to show a higher but not significant weight gain (+3.1 +/- 1.0 kg in group II and +1.9 +/- 0.3 kg in group I). Blood free amino acids were used as rough indicators of amino acid utilization and were analyzed prior and during acute 150 min intravenous infusion of a complete glucose-amino acid mixture. This test was done before and at the end of the experimental periods. Basal essential blood free amino acids were similar in the two groups and did not change during the experimental period. Most essential amino acids increased following glucose-amino acid infusions. The incremental increase was of less magnitude after the experimental period than before when medroxyprogesterone was present (P < 0.05 for valine, leucine, lysine, threonine and methionine). This was not the case in the absence of the hormone. We concluded that medroxyprogesterone might improve the efficacy of an oral protein-rich nutritional support in HIV-infected patients.
Adult↗
Protein synthesis in the perfused rat liver.
1. When the rat livers are perfused under the conditions of these experiments with rat blood diluted with saline, the livers remain capable of removing colloidal chromic phosphate normally for 4 hours or more; that is, the reticuloendothelial system continues to function normally. 2. Good rates of bile flow continue, generally for 4 hours. 3. The livers incorporate radioactivity from the amino acids methionine, lysine, and histidine at rapid rates for 1 or 2 hours. Thereafter the rates fall. 4. The specific activity of the free lysine and histidine in the perfusate falls rapidly during the experiments (to 25 or 35 per cent of its original value at 10 minutes). 5. The fall in rate of incorporation of radioactivity is attributable to the fall in amino acid specific activity. 6. Addition of a complete amino acid mixture to the perfusate does not appear to have any stimulatory effect on incorporation of radioactivity from labelled amino acids. 7. With lysine, on the assumption that incorporation is due to new protein formation, there is a rate of synthesis equivalent to 230 mg. of plasma protein per 100 gm. of rat per day. This result is in agreement with turnover data obtained from rats in vivo. 8. The results emphasize once again the importance of precursor specific activity in the interpretation of metabolic experiments with labelled amino acids.
Amino Acids↗
Influence of protein composition and hydrolysis method on intestinal absorption of protein in man.
An intestinal perfusion technique has been used in normal human subjects to investigate the influence that starter protein composition and hydrolysis procedure have on absorption of amino acid residues from partial enzymic hydrolysates of whole protein. Five starter proteins were studied. Three (egg albumin, casein/soy/lactalbumin, and lactalbumin) were hydrolysed by papain, a second lactalbumin starter protein, and a meat/soy/lactalbumin blend were hydrolysed by a porcine pancreatic enzyme system. Irrespective of starter protein composition or hydrolysis method used, four amino acid residues (threonine, glutamic acid, phenylalanine, and histidine) were absorbed significantly faster from all hydrolysates compared with absorption from their equivalent free amino acid mixtures. In contrast, both starter protein composition and hydrolysis method influenced absorption characteristics of up to nine other amino acid residues.
Adult↗
Sulfur amino acid utilization by growing steers.
Studies were conducted to quantify sulfur amino acid requirements of growing steers. In Exp. 1, six steers (160 kg) were used to determine the methionine requirement in the presence of excess L-Cys. Treatments were abomasal infusion of water only or water plus 2, 4, 6, 8, or 10g/d of L-Met. Steers were fed 2.4 kg/d DM of a diet designed to minimize basal Met supply to the small intestine. Continuous ruminal infusions of VFA (506 g/d) and abomasal infusions of dextrose (150 g/d) increased energy supply to the abomasum. Break-point analysis estimated maximal N retention at 5.8 g/d supplemental L-Met. The basal absorbable Met supply was 2.1 g/d; therefore, the total Met requirement was 7.9 g/d when excess Cys was available. In Exp. 2, five steers (195 kg) were used to determine the efficiency of transsulfuration. Treatments were abomasal infusion of water only or water plus 1.62 or 3.25 g/d L-Cys or 2 o4 g/d L-Met. Diet and infusions were similar to those on Exp. 1, except the amino acid mixture was devoid of Cys and all steers received 4 g/d L-Met to make total sulfur amino acids, but not necessarily Met, limiting. Nitrogen retention increased in response to Met but not Cys infusion and was maximized at 2 g/d supplemental L-Met; thus, the total Met requirement was near 8.4 g/d when the Cys supply was 2.1 g/d. Supplemental Cys did not spare Met, suggesting that nonprotein functions of Met may be quantitatively important.
Abomasum↗
[Parenteral nutrition in liver diseases].
A total parenteral nutrition may particularly be used in patients with liver diseases, for comatous patients or postoperatively. By using central venous catheterization the practical application of high osmolar solutions, fat emulsions and amino acid mixtures is easy to be performed. Partial parenteral nutrition is needed mainly for decompensation of metabolic disturbances of amino acids in liver diseases. As carbohydrates particularly glucose is used, but because of the deranged glucose tolerance also fructose and glucose substitutes are given in mixed solutions. The infusion of fat emulsions partly covers the need of energy and on the other side prevents a lack of essential fatty acids. Recent investigations demonstrated that fat emulsions may be tolerated by patients with liver diseases and fat is utilized for energy metabolism. The changes of plasma amino acids in blood in patients with chronic liver diseases, especially in the stage with liver insufficiency, demands for a special amino acid solution. For the accomplishment of a total as well as for partial parenteral nutrition principles are given and relevant clinical problems are discussed.
Amino Acids↗
[The composition of amino acid-peptide mixtures obtained during hydrolysis of proteins].
The composition of the amino acid and peptide fraction of the protein hydrolyzate and its dependence upon the spray-drying process at elevated temperatures were investigated by GLC and GLC-MS. Spray-drying leads to decrease in the Glu and Met contents, to transformation of Cys into cystine and to formation of lactames (pyroglutamic acid and pyrrolidone) and diketopiperazines. Some dipeptides, acetylproline, paraffines, fatty acid pyridinecarboxylic and lactic acids, ethylene glycol were identified in the fraction. The incidental occurrence of these compounds should be taken into account when investigating the biological activity of protein hydrolyzates.
Amino Acids↗
Amino acid challenge in patients with cirrhosis and control subjects: ammonia, plasma amino acid and EEG changes.
BACKGROUND/AIMS: The pathogenesis of hepatic encephalopathy (HE) is controversial. We have therefore studied the effect of induced hyperammonaemia in man. PATIENTS AND METHODS: 108 g of an amino acid mixture was given orally to 18 cirrhotics and 11 control subjects and changes in blood ammonia, EEG and plasma amino acids were observed. RESULTS: Basal (39+/-6 versus 14+/-2 micromol/l) and 120-min post amino acid (77+/-10 versus 27+/-4) blood ammonia concentrations in cirrhotics were significantly increased compared to healthy controls (p < 0.001). Associated with these changes there was a significant increase in the ratio of slow-to-fast wave activity indicating EEG slowing (+0.41+/-0.16; N=13 versus -0.05+/-0.08; N=8; p=0.036). As expected in cirrhotics, basal valine and leucine concentrations were decreased while phenylalanine, tyrosine and methionine were significantly increased. Although the basal molar ratio of branched chain amino acids to the aromatic amino acids phenylalanine and tyrosine was significantly decreased in cirrhotics (1.5+/-0.2 versus 3.2+/-0.2; p < 0.0001), after the challenge when EEG changes were apparent in cirrhotics, the ratio significantly increased (p < 0.005) in both groups to 2.7+/-0.3 versus 4.1+/-0.3 (p=0.002). In the combined groups, there were significant correlations between EEG ratio change and the 120-min blood ammonia concentration (r=0.498; p=0.022). CONCLUSION: The alterations in plasma amino acid patterns do not support a specific role for any of the amino acid groups in the pathogenesis of hepatic encephalopathy. They are however more in keeping with the direct or indirect role of ammonia.
Adult↗
Facts and fallacies of purported ergogenic amino acid supplements.
Although current research suggests that individuals involved in either high-intensity resistance or endurance exercise may have an increased need for dietary protein, the available research is either equivocal or negative relative to the ergogenic effects of supplementation with individual amino acids. Although some research suggests that the induction of hyperaminoacidemia via intravenous infusion of a balanced amino acid mixture may induce an increased muscle protein synthesis after exercise, no data support the finding that oral supplementation with amino acids, in contrast to dietary protein, as the source of amino acids is more effective. Some well-controlled studies suggest that aspartate salt supplementation may enhance endurance performance, but other studies do not, meriting additional research. Current data, including results for several well-controlled studies, indicated that supplementation with arginine, ornithine, or lysine, either separately or in combination, does not enhance the effect of exercise stimulation on either hGH or various measures of muscular strength or power in experienced weightlifters. Plasma levels of BCAA and tryptophan may play important roles in the cause of central fatigue during exercise, but the effects of BCAA or tryptophan supplementation do not seem to be effective ergogenics for endurance exercise performance, particularly when compared with carbohydrate supplementation, a more natural choice. Although glutamine supplementation may increase plasma glutamine levels, its effect on enhancement of the immune system and prevention of adverse effects of the overtraining syndrome are equivocal. Glycine, a precursor for creatine, does not seem to possess the ergogenic potential of creatine supplementation. Research with metabolic by-products of amino acid metabolism is in its infancy, and current research findings are equivocal relative to ergogenic applications. In general, physically active individuals are advised to obtain necessary amino acids through consumption of natural, high-quality protein foods.
Amino Acids↗