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PubMed1995

Free amino acids exhibit anthozoan "host factor" activity: they induce the release of photosynthate from symbiotic dinoflagellates in vitro.

Reef-building corals and other tropical anthozoans harbor endosymbiotic dinoflagellates. It is now recognized that the dinoflagellates are fundamental to the biology of their hosts, and their carbon and nitrogen metabolisms are linked in important ways. Unlike free living species, growth of symbiotic dinoflagellates is unbalanced and a substantial fraction of the carbon fixed daily by symbiont photosynthesis is released and used by the host for respiration and growth. Release of fixed carbon as low molecular weight compounds by freshly isolated symbiotic dinoflagellates is evoked by a factor (i.e., a chemical agent) present in a homogenate of host tissue. We have identified this "host factor" in the Hawaiian coral Pocillopora damicornis as a set of free amino acids. Synthetic amino acid mixtures, based on the measured free amino acid pools of P. damicornis tissues, not only elicit the selective release of 14C-labeled photosynthetic products from isolated symbiotic dinoflagellates but also enhance total 14CO2 fixation.

Journal Article↗

PubMed1983

Effect of protein quality on dietary induction of hepatic ornithine decarboxylase.

Dietary induction of ornithine decarboxylase (ODC) in rat liver depended on the quality of protein in the diet. Zein did not induce ODC unless it was supplemented with the deficient amino acids, tryptophan and lysine. Similar phenomena were observed with gelatin (tryptophan and methionine) and hemoglobin (isoleucine). However, ODC was found to be significantly induced by an amino acid mixture simulating zein. The difference between amino acid diet and protein diet effects could not be explained by digestibility of zein. Unphysiologically rapid influx of amino acids appeared to induce ODC by a mechanism different from that by which dietary protein induced ODC. After ingestion of zein, the concentration of tryptophan and lysine decreased markedly in plasma and liver. However, it was confirmed that their supply from intracellular protein degradation continued even after feeding. In contrast to ODC, tyrosine aminotransferase was induced by zein as well as by casein, indicating that the requirement of tryptophan and lysine as precursor amino acids for enzyme synthesis was satisfied by reutilization of the amino acids liberated by intracellular protein degradation. Therefore, it was concluded that good quality protein was required for ODC induction mainly as a signal but not as a source of precursor amino acids.

Amino Acids↗

PubMed1987

Amino acid requirements and biological value of proteins for sheep.

An intragastric infusion model was used to determine the biological value of three protein sources for sheep. Biological value was calculated from the regression of urinary nitrogen on nitrogen intake. A casein-amino acid mixture corresponding to previously determined metabolic amino acid requirements as well as casein alone and gelatin was studied. The biological values determined were 1.00 for enriched casein, 0.87 for casein and 0.07 for gelatin. The intercept values, which correspond to the endogenous losses, were approximately 245 mg N/kg 0.75 body weight and did not differ significantly between protein sources or experiments. The data support the proposed metabolic amino acid requirements for sheep for maintenance and wool growth.

Amino Acids↗

PubMed1979

Metabolic and hormonal responses of low birthweight infants to intravenously infused calories not exceeding the maintenance energy expenditure.

Eithe low birthweight infants were studied for their metabolic and hormonal responses to intravenous alimentation when the caloric input was varied. The study was made during three consecutive 12-hour periods, when solutions of glucose, glucose and amino-acids, and glucose and amino-acid and lipids were successively infused. Hypertonic glucose led to a fall in plasma free fatty acids and amino-acids. Supplementation with an amino-acid mixture increased the concentration of amino-acids but not above the fasting level. Thus, hypertonic glucose was an effective means for avoiding hyperaminoacidaemia. Blood urea was little changed, also indicating satisfactory use of amino-acids. The number and distribution of calories infused throughout the third 12-hour period, when lipid was infused, were also important factors contributing to the avoidance of hyperaminoacidaemia. The caloric needs of low birthweight infants kept at neutral temperatures should be individually assessed in the light of recent data. The administration of an unnecessarily large load of calories and nutrients to parenterally-fed infants can thereby be avoided.

Amino Acids↗

PubMed1998

Response of skeletal muscle protein synthesis to insulin in suckling pigs decreases with development.

The elevated rate of muscle protein deposition in the neonate is largely due to an enhanced stimulation of skeletal muscle protein synthesis by feeding. To examine the role of insulin in this response, hyperinsulinemic-euglycemic-amino acid clamps were performed in 7- and 26-day-old pigs. Pigs were infused with 0, 30, 100, or 1,000 ng . kg-0.66 . min-1 of insulin to mimic the plasma insulin levels observed under fasted, fed, refed, and supraphysiological conditions, respectively. Whole body amino acid disposal was determined from the rate of infusion of an amino acid mixture necessary to maintain plasma essential amino acid concentrations near their basal fasting levels. A flooding dose of L-[4-3H]phenylalanine was used to measure skeletal muscle protein synthesis. Whole body amino acid disposal increased progressively as the insulin infusion rate increased, and this response was greater in 7- than in 26-day-old pigs. Skeletal muscle protein synthesis was stimulated by insulin, and this response was maximal at a low insulin infusion rate (30 ng . kg-0.66 . min-1). The stimulation of muscle protein synthesis by insulin was also greater in 7- than in 26- day-old pigs. These data suggest that muscle protein synthesis is more sensitive to insulin than whole body amino acid disposal. The results further suggest that insulin is a central regulatory factor in the elevated rate of muscle protein deposition and the increased response of skeletal muscle protein synthesis to feeding in the neonate.

Amino Acids↗

PubMed1983

Restoration effects of glucose refeeding on reduced synthesis of albumin and total protein and on disaggregated polyribosomes in liver of starved rats: evidence of a post-transcriptional control mechanism.

Previous studies demonstrated that fasting is accompanied with a reduction of liver protein and albumin synthesis. A protein-deficient diet also leads to a marked change in liver RNA and protein metabolism. Although the reduction of protein synthesis and the disaggregated polyribosomes during fasting can be corrected by a single feeding of protein or a complete amino acid mixture, no or little changes of amino acid concentrations were found in portal blood and liver cytosol of fasted animals as compared to those of the fed group. To determine the effect of glucose on the reduced rate of protein and albumin synthesis of fasted rats, free and membrane-bound polyribosomes were isolated quantitatively from liver of starved rats (42-66 h) at different intervals after a single feeding of glucose and after giving glucose ad libitum for 24 h. (1) The yield of polyribosomal RNA decreased dramatically after a 42- to 66-hour starvation. A glucose refeeding did not change the RNA content. However, the restoration of polyribosome size could be observed rapidly. (2) At various levels of RNA, there was a decreased protein synthesis in fasted animals. However, the synthesis was enhanced after glucose refeeding. The albumin synthesis was also proportionately increased (10-12% of total protein synthesis of membrane-bound polyribosomes). (3) Glucose refeeding had no influence on the content of albumin mRNA sequence and liver RNA. These findings suggest that the effect of glucose on the restoration of protein and albumin synthesis is a sole post-transcriptional event.

Albumins↗

PubMed1988

Bioavailability of lysine in L-lysine.HCl.

True digestibility of lysine (LYS) in crystalline L-LYS.HCl and casein determined in cecectomized adult roosters was not significantly different from 100%. Subsequent 9-d growth assays were conducted to determine the bioavailability of LYS in casein, in L-LYS.HCl, and in a mixture of crystalline amino acids simulating casein's amino acid profile. Based on slope-ratio methodology, LYS bioavailability relative to casein was estimated to be 101.4 and 99.9% in L-LYS.HCl and in the casein-simulated amino acid mixture, respectively. Procedures also were developed for assessment of LYS bioavailability in crystalline L-LYS.HCl by comparing growth responses to intraperitoneally injected (IP-LYS) and crop-intubated LYS (CI-LYS) in chicks fed LYS-deficient corn-sesame meal diets. Graded increments of pH-adjusted L-LYS.HCl were administered twice daily in .5-ml doses during the course of 8-d growth assays. Chicks receiving CI-LYS also received .5 ml of IP saline at each dosing, and those receiving IP-LYS also received CI saline at each dosing. Slope-ratio multiple linear regression of gain (g) regressed on LYS administered (mg) was assessed for both ad libitum-fed and meal-fed chicks. Linear growth responses to LYS were obtained with both routes of administration and in both feeding regimens. The CI-LYS slopes ranged from 103 to 125% of those obtained with IP-LYS administration. These results support the view that crystalline L-LYS.HCl is 100% digestible and bioavailable.

Animals↗

PubMed1984

Biological efficacy of liquid methionine and methionine hydroxy analogue-free acid in chicks.

An experiment was conducted to determine biological efficacies of DL-methionine-Na (Liquimeth) and DL-methionine hydroxy analogue (MHA)-free acid (Alimet) relative to DL-methionine in Single Comb White Leghorn male chicks. A crystalline amino acid mixture devoid of sulfur-containing amino acids was used for the basal diet, and the test substances were added at .1, .2, and .3% levels, equivalent to DL-methionine on a molar basis, in place of cornstarch. By a slope ratio assay using chick growth as a criterion, the relative biological efficacies of DL-MHA-free acid and DL-methionine-Na to DL-methionine were found to be 70 and 113%, respectively, on a molar basis.

Animal Feed↗

PubMed1999

Effects of branched-chain-enriched amino acids and insulin on forearm leucine kinetics.

Although amino acid mixtures enriched in branched-chain amino acids (BCAA) and deficient in aromatic amino acids (AAA) are often used together with insulin and glucose in clinical nutrition, their physiological effects on muscle protein anabolism are not known. To this aim, we studied forearm leucine kinetics in post-absorptive volunteers, before and after the systemic infusion of BCAA-enriched, AAA-deficient amino acids along with insulin and the euglycaemic clamp. The results were compared with the effects of insulin infusion alone. A compartmental leucine forearm model was employed at steady state. Hyperaminoacidaemia with hyperinsulinaemia (to approximately 80-100 micro-units/ml) increased the leucine plasma concentration (+70%; P<0.001), inflow into the forearm cell (+150%; P<0.01), disposal into protein synthesis (+100%; P<0.01), net intracellular retention (P<0.01), net forearm balance (by approximately 6-fold; P<0.01) and net deamination to alpha-ketoisocaproate (4-methyl-2-oxopentanoate) (+9%; P<0.05). Leucine release from forearm proteolysis and outflow from the forearm cell were unchanged. In contrast, hyperinsulinaemia alone decreased plasma leucine concentrations (-35%; P<0.001) and leucine inflow (-20%; P<0.05) and outflow (-30%; P<0.01) into and out of forearm cell(s), it increased net intracellular leucine retention (P<0.03), and it did not change leucine release from forearm proteolysis (-20%; P=0.138), net leucine deamination to alpha-ketoisocaproate, leucine disposal into protein synthesis or net forearm protein balance. By considering all data together, leucine disposal into protein synthesis was directly correlated with leucine inflow into the cell (r=0.71; P<0.0001). These data indicate that the infusion of BCAA-enriched, AAA-deficient amino acids along with insulin is capable of stimulating forearm (i.e. muscle) protein anabolism in normal volunteers by enhancing intracellular leucine transport and protein synthesis. These effects are probably due to hyperaminoacidaemia and/or its interaction with hyperinsulinaemia, since they were not observed under conditions of hyperinsulinaemia alone.

Adult↗

PubMed1975

Dissociation of lipid and protein from cell-DNA by direct alkaline sucrose gradient analysis.

Hela cells and normal human embryo cells were analyzed in alkaline sucrose gradients after labeling with 14C-thymidine and 3H-choline chloride or 3H-amino acid mixture. Radioactivities from both choline and amino acids were observed in accord with DNA peak when the labeled cells were analyzed after 1 or 2 hour lysis in the lysing solution at 25 degrees C; i.e., a sharp and high peak observed with HeLa cells and a peak with more reduced sedimentation rate observed with normal human embryo cells could be considered to indicate the association of DNA with lipid and protein components, probably the nuclear membrane. The peak which was obtained after 4 hour lysis at 25 degrees C or after 1 hour lysis at 37 degrees C was not associated with label from choline and amino acids and, thus, proved to have been released from lipid and protein fractions. When metaphase HeLa cells were collected after labeling with choline or amino acids and then analyzed, the radioactivity was demonstrated in the sharp and high peak after 1 or 2 hour lysis at 25 degrees C; that is, the lipid and protein portions might be somehow associated with the mammalian metaphase chromosomes.

Cells, Cultured↗

PubMedDate not supplied

[Effect of the composition of branched chain amino acids, taurine, and tryptophan on the amino acid metabolism in experimental models of alcoholism].

Ethanol withdrawal after forced alcoholization of rats according to Majchrowicz led to the development of amino acid imbalance in the pool of free amino acids in the liver (increasing levels of alanine, aspartate, glutamate, glutamine and histidine, decreasing levels of glycine, lysine, threonine and taurine) and blood plasma (increasing levels of tyrosine and alanine, decreasing levels of most glycogen aminoacids, branched-chain aminoacids and Lys). Less profound changes were observed after prolonged alcohol intoxication (decreasing levels of alanine, ornitine, citrulline and increasing level of Glu in liver, increasing levels of sulfur-containing compounds, Asp and Lys in blood plasma). Amino acid mixture which contained branched-chain amino acids, taurine and tryptophan administered intragastrically was found to correct levels of sulfur-containing amino acids, threonine, lysine and isoleucine after ethanol withdrawal and to eliminate disorders in urea cycle, exchange of threonine, glycine and phenylalanine after prolonged alcohol intoxication.

Administration, Oral↗

PubMed1987

Influence of tryptophan availability on selection of alcohol and water by men.

To study the effects of tryptophan on alcohol selection the tryptophan levels in subjects were altered through the administration of amino acid mixtures. Male social drinkers (N = 45) with no psychiatric or medical problems were divided into three groups and consumed a drink that contained, respectively, a nutritionally balanced amino acid mixture, a tryptophan-supplemented mixture, or a tryptophan-free mixture. After a waiting period of 5 hours, blood samples were taken and subjects participated in an ad-lib taste rating of six--one nonalcoholic and five alcoholic--beverages. Water was also made available to subjects. Although there was a marked effect on total and free plasma tryptophan levels showing a dramatic increase in the case of the tryptophan-supplemented group and a decrease in the tryptophan-free group, altered tryptophan levels did not influence the amount of alcohol subjects ingested. Tryptophan supplementation was found to decrease water intake significantly by an unknown mechanism without affecting alcohol selection.

Adolescent↗

PubMed1976

Biological assessment of protein quality. Optimal essential: non-essential amino acid ratios for maintenance of certain states of nitrogen balance in young rats.

Male weanling rats were used to assess the effect of replacing essential amino acid (EAA) mixtures with non-essential amino acid (NEAA) mixtures on nitrogen balance. Each of 4 essential amino acid mixtures, fed in quantities sufficient to maintain specific states of nitrogen balance, was replaced with a non-essential amino acid mixture on an isonitrogenous basis. The results indicate the following: 1. Within limits, replacement with NEAA mixture caused an increase in the efficiency of utilisation of the amino acid mixture when the nitrogen balance state investigated was + 100, +200 or +300 mg/100 g body mass/8 days, but not when nitrogen balance was zero. 2. In the maintenance of nitrogen balance = 0, the EAA mixture could be replaced with NEAA mixture to a greater extent (83%) than was possible in the maintenance of balance states of + 100, +200 or +300 mg (about 70%). The results support the view that (a) EAAs are converted to NEAAs at the cost of metabolically available nitrogen: and (b) with a decrease in the state of nitrogen balance maintained by the animal, the amino acid requirement is shifted partially from EAAs to NEAAs. The implications of the above findings are discussed with reference to dietary protein evaluation and related questions.

Adaptation, Physiological↗

PubMed1995

Microdialysis as a tool to measure dietary and regional effects on the complete profile of extracellular amino acids in the hypothalamus of rats.

Regional and dietary-induced changes in hypothalamic extracellular amino acid concentrations were examined. Microdialysis probes were simultaneously implanted in the hypothalamic paraventricular nucleus (PVN) and the lateral hypothalamus (LH) of anesthetized rats and perfused at a rate of 2 microliters/min. Dialysates were collected every 20 min for 1 h prior to gavage of a balanced amino acid mixture (0.85 g patterned after 1 g of chicken egg albumin) and then every 20 min for 3 h after treatment. Tail vein blood samples were also collected. Marked changes in plasma levels of most amino acids were evident immediately following the amino acid gavage. In the PVN, concentrations of isoleucine, leucine, methionine and valine all increased within 40 min, whereas significant decreases in glutamine, histidine and taurine were observed in the LH. In a separate study, PVN extracellular amino acid concentrations were examined in awake, freely-behaving rats following gavage of equicaloric loads of a balanced amino acid mixture, glucose (0.89 g) or water. Dialysate levels of glutamate, isoleucine, leucine, methionine, threonine, tyrosine and valine showed reliable increases after amino acid treatment, although the overall time course of these effects differed somewhat. The amino acid profile of the PVN was, in general, unaffected by glucose administration. These findings suggest that specific brain regions may respond uniquely to amino acid ingestion and further imply that dietary composition may influence the amino acid profiles of the extracellular fluid in brain.

Amino Acids↗

PubMedDate not supplied

[Electrokinetic potential of cell nucleus during changes in the functional activity of rat hepatocytes].

There were investigated changes of electrokinetic potential (EKP) of hepatocyte nuclei during hydrocortisone induction and activation induced with amino acids mixture. An increase of RNA-polymerase activity was shown to correlate with EKP value. Actinomycin D essentially decreased this potential. Injection of hydrocortisone or amino acids mixture under the suppression of transcription with actinomycin D removed the inhibitor action, but the potential value did not reach that under the action of the activators only. Induction with hydrocortisone increased the potential by various degrees for the nuclei of different size. The results obtained suggest that EKP of the nuclei carries the information about functional condition of the genetic apparatus and can be a valuable and handy instrument of definition of its physiological activity.

Animals↗

PubMed1996

Functional crown ether derivatives as sorbents for ligand exchange chromatography.

Two kinds of macrocyclic compounds, S-TAROH18C6 and S-TAROEt12C4 derived from tartaric acid have been synthesized. The structure and conversion of functional groups on this silica gel based resin have been confirmed by IR spectral and elemental analysis. The coordination behaviour of these materials has been investigated by means of IR, EPR, potentiometry and the modification of Langmuir isotherm equation. The metal complexes have been investigated as stationary phases for the separation of amino acid mixtures. Factors affecting the retention and the sample selectivity have been examined. S-TAROEt12C4 possesses good chromatographic characteristics and a unique selectivity in separating underivatized amino acid mixtures and can be used as well for enantiomeric separations.

Journal Article↗

PubMed1975

The role of plasma amino acids in hepatic encephalopathy.

The dog with an end-to-side portacaval shunt has a plasma amino acid pattern similar to that in man with chronic liver disease and encephalopathy. When dogs with end-to-side portacaval shunts manifested symptoms of hepatic encephalopathy, superior caval catheters were placed and one of three solutions was infused. Whereas almost all animals given a commercially available synthetic amino acid mixture died, a special mixture formulated to normalize plasma amino acids was associated with 100 percent survival and few neurological symptoms. The results suggest that manipulation and normalization of plasma amino acids in animals with hepatic failure may be efficacious in providing adequate nutrition while minimizing hepatic encephalopathy. Moreover, these experiments may shed some light on the mechanism of human hepatic encephalopathy.

Albumins↗

PubMed1989

Mechanism and regulation of protein degradation in liver.

The degradation of intracellular protein and other cytoplasmic macromolecules in liver is an ongoing process that regulates cytoplasmic mass and provides amino acids for energy and other metabolic uses early in starvation. Cellular proteins are conveniently divided into two general classes according to readily discernable differences in average rates of turnover. A short-lived class, having a half-life of approximately 10 min, comprises about 0.6% of total protein. Its degradation is not physiologically controlled, and the mechanism is probably nonlysosomal in nature. The second or long-lived group, with an average half-life 250 times greater, constitutes more than 99% of the cell's protein. By contrast, its breakdown is strongly regulated, and the site of catabolism is believed to be the vacuolar-lysosomal system. Cytoplasmic sequestration by lysosomes can be divided into two categories; macro- and microautophagy. The first is induced by amino acid and/or insulin deprivation. Amino acids are considered to be primary regulators, since they can control this process over the full range of induced proteolysis in the absence of hormones. Glucagon, cyclic AMP, and beta-agonists also stimulate macroautophagy in hepatocytes but have opposite effects in myocytes. Micrautophagy differs from the former in that the cytoplasmic "bite" is smaller and the uptake process is not acutely regulated. However, the latter does decrease during starvation in parallel with basal proteolysis, effects that might be linked to the loss of endoplasmic reticulum. The primary control of macroautophagy is accomplished through a small group of direct regulators (Leu, Tyr/Phe, Gln, Pro, Met, His, and Trp) and a specific coregulatory action of alanine. As a group, regulatory amino acids produce direct inhibitory responses in the perfused rat liver that are identical to those of the complete amino acid mixture at 0.5x and 4x (times) normal plasma concentrations. However, they lose effectiveness almost completely within a narrow zone centered at normal levels, a loss that can be abolished by the addition of alanine at its normal plasma concentration (0.5 mM). At this level, alanine does not inhibit directly. Interestingly, this zonal loss is also eliminated by insulin. Glucagon, though, specifically blocks the initial inhibition evoked by 0.5x amino acid mixtures and thus induces maximal rates of protein degradation at normal amino acid concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acids↗