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PubMed1981

Evidence that transpeptidation is a significant function of gamma-glutamyl transpeptidase.

gamma-Glutamyl transpeptidase (purified from rat kidney) was incubated with glutathione and a mixture of amino acids that closely approximates the amino acid composition of blood plasma, and the relative extents of transpeptidation and hydrolysis were determined by quantitative measurement of the products formed (glutamate, cysteinylglycine, gamma-glutamyl amino acids). At pH 7.4, in the presence of 50 microM glutathione and the amino acid mixture, about 50% of the glutathione that was utilized participated in transpeptidation. Studies in which the formation of individual gamma-glutamyl amino acids was determined in the presence of glutathione and the amino acid mixture showed that L-cystine and L-glutamine are the most active amino acid acceptors, and that other neutral amino acids also participate in transpeptidation to a significant extent. These in vitro experiments are consistent with a number of other findings which indicate that transpeptidation is a significant physiological function of gamma-glutamyl transpeptidase.

Animals↗
PubMed1982

Dynamics of insulin and glucagon secretion by the isolated perfused cat pancreas.

1. The dynamics of insulin and glucagon secretion by the isolated perfused cat pancreas was studied in response to glucose and amino acid stimuli. 2. Insulin secretion is biphasic in response to either glucose or amino acid stimuli. 3. Glucose caused a much more pronounced first phase release than did a complete amino acid mixture; whereas glucose and the amino acid mixture stimulated late second phase insulin secretion equipotently. 4. The same amino acid mixture produced a biphasic secretion of glucagon characterized by a rapid and transient spike-release which was followed by a substantial, relatively steady-state, second secretory phase. 5. Various combinations of glucose and amino acids resulted in insulin secretion which suggests a simple additive stimuli phenomenon; whereas no such additive effect was observed with respect to amino acid stimulation of glucagon secretion. 6. Instead, various of the amino acids appear to stimulate maximal glucagon secretion independently. 7. Glucose failed to cause a suppression of amino acid induced glucagon release. 8. The quantitative aspects of this study suggest that the cat pancreas is very responsive to amino acid modulation of hormone release, a fact which may well reflect the high amino acid content of the cat's diet.

Amino Acids↗
PubMed1987

[Studies on the absorption of elemental diets containing "small peptides" as a nitrogen source].

Previous studies have shown that small peptides (di-or tri-peptide) are more rapidly and more evenly absorbed through the small intestine than free amino acid mixture of the same amino acid composition. Since a method to produce protein hydrolysate rich in di-or tri-peptide (SP) was developed, absorption studies were performed to ascertain if the SP shows superior efficiency in absorption to the free amino acid mixture (AA) and large peptide (LP) of the same amino acid composition. A practical elemental diet which contained SP as a nitrogen source, was made (SP-ED) and the absorption rates of nitrogen, carbohydrate and water were studied using dog Thiry-Vella loop in comparison with ED prepared with AA (AA-ED) or LP (LP-ED) with the same amino acid composition. The results are as follows: 1) Absorption rates of nitrogen and water in SP were higher than in AA and LP, when the osmolarities of these solutions were not adjusted to the same level. 2) When the osmolarities of the solutions were adjusted to the same level using mannitol, the absorption rate of nitrogen was still the highest in SP. 3) Nitrogen absorption rate was significantly higher in SP-ED than in AA-ED and LP-ED and carbohydrates were absorbed to a significantly greater extent from the SP-ED than from the AA-ED. These results indicate that small peptides are suitable for use as the nitrogen source for ED.

Animals↗
PubMed1999

Facial taste responses of the channel catfish to binary mixtures of amino acids.

We investigated the neural processing of binary gustatory mixtures of amino acids by the facial taste system of the channel catfish, Ictalurus punctatus. In vivo electrophysiological recordings indicated that the magnitude of both integrated and single-unit facial taste responses to binary mixtures of amino acids was greatest if the components bound to independent receptor sites. Facial taste responses were obtained from 32 multiunit and 55 single taste fiber preparations to binary mixtures of amino acids whose components bind to independent taste receptor sites (group I) or to the same or highly cross-reactive taste receptor sites (group II). All component stimuli were adjusted in concentration to provide approximately equal response magnitude as determined by either the height of the integrated multiunit taste response or by the number of action potentials generated/3 s of response time/single taste fiber. The mixture discrimination index (MDI), defined as the response to the mixture divided by the average of the responses to the component stimuli, was calculated for each test of a binary mixture. MDIs of group I binary mixtures for both the integrated multiunit and single fiber data were significantly greater than those for either the control or group II binary mixtures. In a subset of multiunit recordings, the MDIs of a group I binary mixture across three log units of stimulus concentration were similar and significantly greater than those of a group II binary mixture. Analysis of the single fiber data also indicated that the MDIs of group I binary mixtures were significantly larger than those of group II binary mixtures for both alanine-best and arginine-best taste fibers; however, the MDIs of group I binary mixtures calculated from recordings from arginine-best taste fibers were significantly greater than those recorded from alanine-best taste fibers.

Amino Acids↗
PubMed1982

Exogenous amino acids as fuel in shock.

It has been suggested that in shock branched-chain amino acids are preferentially oxidized resulting in continued proteolysis and stimulated gluconeogenesis. To determine if exogenous amino acids could be used as fuel in shock, dogs rendered hypotensive by controlled cardiac tamponade and normotensive controls were infused with amino acid mixtures and individual amino acids. When Nephramine, a mixture rich in branched-chain amino acids, was infused, plasma alpha-amino nitrogen levels rose but urea output did not increase in either the control state or in shock, suggesting that these amino acids were not rapidly deaminated to serve as fuels. Travasol, which in addition contained large amounts of alanine and glycine, tripled urea output in the controls and doubled it in shock. The limit of urea production was reached in both groups at 35 mumoles urea/minute/kg. In the Travasol-infused animals plasma alpha-amino nitrogen levels were maintained in normotension but rose sharply in shock. When glycine alone was infused into five dogs in shock urea production rate was 30.6 + 2.1 mumoles/minute/kg; with alanine the same value was 22.5 + 2.2 mumoles/minute/kg. In both cases plasma alpha-amino nitrogen levels were high, suggesting that transport of these amino acids into the cell was slow in shock. In four dogs in shock glycine-14C was added to the glycine infusate as a tracer. At radioactive equilibrium 28% of the label infused appeared in CO2; another 22% appeared in glucose. It is concluded that of all the amino acids tested only glycine and alanine are deaminated rapidly enough to serve as exogenous fuels in shock.

Alanine↗
PubMed1988

Oligopeptide mixtures produced from soy protein by enzymatic modification and their nutritional qualities evaluated by feeding tests with normal and malnourished rats.

Soy protein isolate (SPI) was enzymatically modified to produce oligopeptide mixtures having methionine at approximate levels of 1% and 3%. Each of them had an average molecular weight of slightly lower than 1,000 daltons. They were compared with corresponding amino acid mixtures as well as with SPI for protein efficiency ratio (PER) and several other parameters. Normal and protein-malnourished rats were used as subjects for the comparison tests. When malnourished rats were subjected to a feeding test at a methionine level of 1% in nitrogen source, the oligopeptide mixture, OPM1, gave a significantly higher PER value than any of SPI and the amino acid mixtures. At a methionine level of 3%, both normal and malnourished rats utilized the oligopeptide mixture, OPM3, with higher efficiency than the amino acid mixture. These results suggest that the oligopeptide mixtures were utilized similarly to or more efficiently than SPI from which they were derived and the amino acid mixtures with exactly simulated amino acid composition.

Amino Acids↗
PubMedDate not supplied

Fibronectin levels in stressed and septic patients fed with total parenteral nutrition.

Plasma fibronectin concentrations were measured in healthy persons as well as in septic and stressed patients. A decrease in plasma fibronectin concentration was shown in volunteers receiving a low energy (600 kcal), amino acids- and lipid-deficient diet. Increased fibronectin levels were measured in stressed and septic patients, not receiving enteral nutrition, after adequate total parenteral nutrition (TPN during 1 week). It is concluded that total parenteral nutrition facilitates improved fibronectin synthesis in stressed and septic patients. Total parenteral nutrition containing an amino acid mixture rich in branched amino acids (50.2% BCAA) is not superior to TPN containing a standard amino acid mixture (15.6% BCAA) in this respect.

Adult↗
PubMed1975

Chemical stimulatory mechanism in gastric secretion.

1. The serum gastrin level, gastric mucosal blood flow and acid secretion from the canine Heidenhain pouch have been measured in response to the introduction of bovine serum albumin, pepsin-digested albumin, an amino acid mixture, liver extract and mannitol used as control. 2. Distention of the Heidenhain pouch with mannitol or albumnin at pH 5-0 produced a similar pressure-related increase of acid secretion reaching a peak of only 10 percent of the maximal response to histamine. Pepsin-digested albumin was capable of producing larger acid outputs than undigested albumin. The highest acid output, attaining about 80 percent of the maximal response to histamine, was obtained with liver extract both before and after exhaustive dialysis to remove all the amino acids and short peptide fragments. An amino acid mixture containing all essential amino acids was also found to stimulate acid secretion but a lesser degree than liver extract. 3. This concluded that it is not the intact protein but the products of its digestion, the polypeptides and free amino acids, which are potent chemical stimulants of acid secretion from the oxyntic gland area. Since the serum gastrin level was not changed during acid secretion induced by peptic digests bathing the oxyntic gland area, the mechanism of chemical stimulation appears to be gastrin-independent. 4. The response to chemical stimulation by peptic digests can be greatly potentiated by combining this with distention of the oxyntic gland area. Topical application of xylocaine or atropine causes a marked decrease of Heidenhain pouch response to peptic digests, suggesting a possible neural reflex component in the mechanism of chemical stimulation of the oxyntic gland area. 5. When the pH of the liver extract in the Heidenhain pouch was gradually decreased in sequential order from 5-0 to 1-0, this resulted in a pH-related decrease in acid secretion and in the mucosal blood flow falling to the basal level at pH 1-0. Exogenous secretion given in graded doses from 0-5 to 8-0 u./kg. hr caused a small but dose-related inhibition of acid response to liver extract accompanied by a decrease of mucosal blood flow but without any significant change in the serum gastrin level. 6. The results indicate that the chemical stimulation of the oxyntic gland area by peptic digests is capable of inducing acid secretion by a local, gastrin-independent, partially neural reflex mechanism; sensitive to pH, pressure and secretin.

Albumins↗
PubMed1976

Plasma amino acids in reptiles after feeding protein or amino acids and after injecting amino acids.

Turtles (Pseudemys scripta elegans) and alligators (Alligator mississipiensis) were fed fish, casein, or free amino acid mixtures, or were injected with free amino acid mixtures, quantities in each case being equivalent to about 42 mmoles of amino acids/kg body weight. The experiments were designed to determine whether protein synthesis normally precedes catabolism of the amino acids absorbed from digesting food. Both animals disposed of free or food-derived amino acids more rapidly than could be accounted for by catabolism alone, but the transient increases in turtle plasma concentrations consisted mostly of essential amino acids, whereas the alligator plasma showed little increase in essential amino acids and considerable rises in four nonessential amino acids, glutamine, glutamic acid, glycine and alanine. Despite some species variation, these two species with low metabolic rates apparently utilized protein synthesis to dispose of amino acid mixtures prior to the necessarily slow process of catabolism for energy.

Administration, Oral↗
PubMed1986

Relationship between amino acid composition of diet and plasma cholesterol level in growing rats fed a high cholesterol diet.

The effects of dietary sulfur-containing amino acids and glycine on plasma cholesterol level were studied in rats fed amino acid mixture diets containing cholesterol. The relationship between the amino acid composition of dietary proteins and plasma cholesterol levels was also investigated in rats fed diets containing various kinds of protein such as casein, egg albumin, pork protein, fish protein, corn gluten, wheat gluten and soy protein. Feeding the amino acid mixture corresponding to casein led to an approximately two-fold level of plasma total cholesterol as compared with feeding the amino acid mixture corresponding to wheat gluten. It was possible to reduce the plasma cholesterol of rats fed the amino acid mixture of the casein type by increasing the proportion of cystine in the total sulfur amino acids. Inversely, the deprivation of cystine resulted in an enhancement of the plasma cholesterol of rats fed the gluten type amino acid mixture. Glycine had a tendency to resist increases in the plasma cholesterol level. A significant negative correlation was noted between plasma cholesterol levels and the content of cystine in intact dietary proteins. The results suggest that the differential effect of dietary proteins on plasma cholesterol level is mainly associated with sulfur-containing amino acids included in the protein, regardless of whether it is of animal or plant origin.

Amino Acids↗
PubMed1993

Regulation of RNA degradation in cultured rat hepatocytes: effects of specific amino acids and insulin.

The regulation of RNA degradation by specific amino acids and insulin was investigated in cultured rat hepatocytes from fed rats previously injected in vivo with [6-(14)C]orotic acid. The effects of three groups of amino acids were compared to those of a complete amino acid mixture. The first one consisted of the eight amino acids (leucine, proline, glutamine, histidine, phenylalanine, tyrosine, methionine, tryptophan) previously found to be particularly effective in the control of proteolysis. The two other groups were defined from our study with single additions of amino acids, one consisting of proline, asparagine, glutamine, alanine, phenylalanine, and leucine and the other including the latter group with serine, histidine, and tyrosine. The results showed that these three groups were able to strongly inhibit deprivation-induced RNA breakdown at one and ten times normal plasma concentrations but to a lower extent than the complete amino acid mixture. Six amino acids (proline, asparagine, glutamine, alanine, phenylalanine, leucine) inhibited individually RNA degradation by more than 20%. However, the deletions of proline, asparagine, glutamine, or alanine from the group of these six amino acids were not followed by a loss of inhibitory effect. On the contrary, an important loss of inhibition was observed when leucine and phenylalanine were deleted. Furthermore, only these two amino acids exhibited an additive inhibitory effect. Thus leucine and phenylalanine could be considered as important inhibitors of RNA breakdown in cultured rat hepatocytes. Finally, insulin which had no significant effect on RNA degradation in the absence of amino acids, was able to potentiate the inhibitory effect of different amino acid groups.

Amino Acids↗
PubMedDate not supplied

[Use of the urea increment as an index of the effectiveness of parenteral feeding].

The influence exerted by the composition of intravenously introduced mixture of amino acids on so-called urea increment, i.e. the difference between the urea concentration in the blood on an empty stomach an on termination of its introduction, was studied in tests on adult mongrel male-dogs. On the other hand, upon introduction of an amino acids mixture imitating the Swedish preparation Vamin, which includes all essential and non-essential amino acids (except for glutamine and asparagine) in proportion as found in the egg white the urea increment values turned out to be inferior than on administration of a mixture containing from among essential amino acids only arginine and histidine, and from among non-essential ones-glycine and glutamic acid. The urea increment was also lower following combined introduction of an amino acids mixture together with an energy-producing (calorific) material, than when the latter was fed on prior to introduction of the mixture. The totality of findings suggests that as to its sensitivity to the composition of the parenterally introduced nutritional mixture and, possibly, dietary regimen-the urea increment is in no way inferior to the cumbersome, and difficulty realizable under clinical conditions method of nitrogen balance as a criterion for the efficacy of parenteral nutrition and deserves a detailed study as regards its clinical application.

Amino Acids↗
PubMed1979

Regional brain studies on indoles and tyrosine in Mongolian gerbils during nutrition with artificial mixtures high in branched chain amino acids compared to a protein rich diet.

Up till now evidence is lacking regarding the regional distribution of indoles, like tryptophan (TRP), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) as well as tyrosine (TYR) in the brains of Mongolian gerbils. Therefore using a microdissection technique and pooling regional brain samples, it can be shown that there is a regional distribution of 5-HT and 5-HIAA in the brain of Mongloian gerbils which is highest in the raphe + reticular formation system followed by the rest of the brainstem and lenticular nuclei. A longterm fast (22 hours) increases TRP and 5-HIAA but not 5-HT, indicating an increase in the turnover rate of 5-HT. Brain TYR and TRP are only slightly increased after a protein rich diet, whereas 5-HT and 5-HIAA are not changed. Artificial nutrition with amino acid mixtures highly concentrated with branched chain amino acids lead to a decrease of TYR and TRP as well as 5-HT and 5-HIAA. Competing amino acid as well as inhibition of 5-HT synthesis is suggested to be responsible for these effects. Mongolian gerbils show higher brain values of TRP and lower ones of TYR in comparison with other species of mice. In peripheral organs, specially in the liver and lung, similar effects are observable. However, the changes are only mild in comparison to that observed in the brain. Moreover, TYR and TRP are significantly increased in peripheral organs after a protein rich diet.

Amino Acids, Branched-Chain↗
PubMed2000

The behavioral detection of binary mixtures of amino acids and their individual components by catfish.

The question of whether a binary mixture of amino acids is detected by fish as a unique odor or whether the qualities of the individual components are retained within the mixture was investigated in channel (Ictalurus punctatus) and brown bullhead (Ameiurus nebulosus) catfish, species that are highly similar in their olfactory receptor and behavioral responses to amino acid odorants. Catfish respond with greater appetitive food-searching (swimming) behavior to amino-acid-conditioned olfactory stimuli than to non-conditioned amino acids. In the present study, appetitive food-searching behavior was measured by counting the number of turns of the fish greater than 90 degrees within 90 s of stimulus onset and, in some tests, by video tracking. The two methods yielded highly correlated results. Channel catfish conditioned to a binary mixture composed of equimolar amino acids responded with searching behavior to the amino acid that produced the larger-amplitude electro-olfactogram (EOG) response as they did to the conditioned stimulus. In further studies, bullhead catfish were conditioned either to a binary mixture or to a single amino acid and tested to determine whether a binary mixture was detected as the component evoking the larger EOG response. In all initial tests (trials 1-3), the more stimulatory component of a binary mixture was not discriminated from the binary mixture; however, the less stimulatory component and all other amino acids tested were discriminated from the mixture. By increasing the concentration of the originally less potent component in a binary mixture, making it the more stimulatory compound, it was now detected as not significantly different from the binary mixture; however, the original more potent component (i.e. now the less potent stimulus) was detected as significantly different from the mixture. However, with 5-10 additional discrimination training trials, the less stimulatory component in a binary mixture influenced the perception of the binary mixture because the binary mixture was no longer detected only as its more stimulatory component. The data suggest that a two-step learning process occurs within the olfactory bulb and possibly higher-order telencephalic nuclei.

Amino Acids↗
PubMed1986

A concentrated mixture of amino acids and dipeptides for total parenteral nutrition.

Using a subhuman primate (baboon) we have investigated the utility of a 20% mixture of amino acids and dipeptides as the nitrogen source for total parental nutrition. The mixture, besides containing all 8 essential amino acids and a number of non-essential amino acids (glutamate, aspartate, arginine, histidine, serine, ornithine and alanine), contained 6 dipeptides (Gly-Ile, Gly-Leu, Gly-Val, Gly-Tyr, Gly-Gln, and Ala-Gln) and acetyl-cysteine. A week of total parenteral nutrition was preceded by one week of oral feeding. The caloric intake and composition during the two periods was identical except for the nitrogen source, which was intact protein during the oral period, and the mixture of amino acids and dipeptides during the parenteral period. There was no significant difference between gain in body weight or nitrogen balance during the two periods. There were selective increases in plasma and muscle concentrations of amino acids during the parenteral period, which appeared to reflect the amino acid enrichment of the nitrogen source. The efficient utilization of dipeptides was evidenced by their small concentrations in plasma and urine. The urinary excretion of dipeptides was about 1% of the amount infused. This efficiency of dipeptide utilization persisted even when the infusion rate of the amino acid and dipeptide mixture was increased by 7-fold. There was no alteration in liver, kidney, and immune function during the parenteral period. The data indicate the efficacy and safety of the mixture of amino acids and dipeptides as the nitrogen source for parenteral nutrition.

Amino Acids↗
PubMed1994

Mood-lowering effect of tryptophan depletion. Enhanced susceptibility in young men at genetic risk for major affective disorders.

METHODS: A double-blind placebo-controlled cross-over study in which plasma tryptophan was manipulated by administration of a tryptophan-deficient amino acid mixture. In the placebo condition, all subjects received a nutritionally balanced amino acid mixture that contained tryptophan. To further standardize baseline amino acids, each subject was provided with a low-protein diet the day before amino acid challenges. Subjects were euthymic, healthy men aged 18 to 30 years with either a multigenerational family history of affective illness or no family history of psychiatric illness in the present or in the two previous generations. Each subject was screened with a structured clinical interview to rule out a personal history of psychiatric illness. RESULTS: Plasma tryptophan was reduced by 89% 5 hours after the administration of the tryptophan-deficient amino acid mixture. Six of 20 subjects with a family history of affective illness and none of 19 subjects without a family history of psychiatric illness showed a lowering of mood of 10 or more points on the Profile of Mood States depression scale (P = .012, Fisher's Exact Test) 5 hours after tryptophan depletion. No significant mood changes were observed following the control treatment (balanced amino acid mixture) in either group. CONCLUSIONS: Our data support the hypothesis that subjects with no prior depressive episodes but with a multigenerational family history of major affective disorder show a greater reduction in mood after tryptophan depletion. They are also consistent with theories that implicate deficient serotonergic function as one possible etiological factor in major depressive disorders.

Adolescent↗
PubMed1985

[Comparative studies on the enzymatic absorption of protein hydrolysates in the small intestine of the rat. 3. The absorption trypsins thermatatic and trypsin-thermatatic hydrolysates of a fava bean protein isolate compared to an equimolar mixture of free amino acids].

Tryptic, thermitatic, and tryptic-thermitatic Faba bean protein hydrolyzates as well as their equimolar mixture of amino acids were perfused through proximal and distal parts of the intestine (10 cm length) of non-narcotized rats. The total amino-acid concentration of the perfused solution was 50 mM. The absorption of nitrogen and total amino acids from the tryptic and tryptic-thermitatic hydrolyzates was lower than that from the amino-acid mixture, the absorption from the thermitatic hydrolyzate was in accordance with that from the amino-acid mixture. The absorption pattern of the amino acids which preferably undergo a peptidic absorption is similar with the three hydrolyzates: in the proximal intestinal part this concerns glutamic acid and serine, in the distal intestinal part--methionine, alanine, glycin, and serine. The absorption pattern of the amino acids is different between the three hydrolyzates and the amino-acid mixture. Between the absorption pattern of the amino acids from the three hydrolyzates little differences were evident only in the proximal intestinal part. The coefficients of variation of the tryptic-thermitatic hydrolyzates are in accordance with those of the amino-acid mixture, whereas that of the thermitatic hydrolyzates is significantly lower. In the distal intestinal part all supplied forms are more rapidly absorbed than in the proximal part of the intestine.

Amino Acids↗