Tissue Free Amino Acid Pool Research Articles

Changes in tissue free amino acid pools in growing chickens fed thermally treated vetch diets

A three-day assay was developed to evaluate the effect of autoclaving on protein quality of vetch as an alternative to classical growth methods. Male chickens (n = 10/diet) were given approximately isonitrogenous diets based on raw or autoclaved vetch for 3 days. Samples of plasma, muscle and liver were obtained for free amino acid analysis. Heating vetch depressed growth (11.9 vs. 23.2 g/d; p < 0.05). Plasma methionine and histidine increased (0.05 < p < 0.06), while gluconeogenic amino acids tended to decrease (p < 0.10) after heating. Muscle free amino acids did not change except for a trend to increased methionine (p = 0.06) in birds fed autoclaved vetch. In liver, most essential amino acids, glycine, proline and tyrosine increased markedly with heated vetch diet. Correlations between plasma and muscle free amino acids were poor compared with those between plasma and liver free amino acids. Liver free amino acid pool was more sensitive than muscle or plasma pool to amino acid inflow modifications after vetch heating.

Measurement of protein fractional synthesis and breakdown rates in the skin of rabbits using a subflooding dose method

The flooding dose method continues to be useful in measuring protein fractional synthetic rate (FSR) in a tissue. However, flooding of free amino acid pools eliminates enrichment difference between plasma and tissue free amino acid pools, which makes it impossible to concomitantly measure protein fractional breakdown rate (FBR). We hypothesized that a subflooding dose of an amino acid reduces the enrichment difference between plasma and tissue free amino acid pool to a minimal measurable level, thus allowing concomitant measurement of protein FSR and FBR. Phenylalanine (40% enriched) at 50 mg/kg was intravenously injected as a bolus in 6 anesthetized rabbits. Arterial blood and chest skin samples were taken before the injection and for 120 minutes after the injection. Fractional breakdown rate of skin protein calculated from 15-60-120–minute sampling times was 11.3%/d ± 2.0%/d, which was close (P = .66) to the corresponding FSR of 10.0%/d ± 2.3%/d. The subflooding dose injection did not disturb the FBR approach because modifications on the FBR equation to account for the changes of plasma phenylalanine concentration resulted in the same value (11.5%/d ± 1.4%/d). The FBR was positively correlated with the FSR (r = 0.80, P < .05). These findings indicate maintenance of protein mass in the skin, which is a metabolic characteristic of the skin. This subflooding dose method provides a methodological choice to concomitantly measure both FSR and FBR in a tissue.

Branched-chain amino acid supplementation during bed rest: effect on recovery.

Bed rest is associated with a loss of protein from the weight-bearing muscle. The objectives of this study are to determine whether increasing dietary branched-chain amino acids (BCAAs) during bed rest improves the anabolic response after bed rest. The study consisted of a 1-day ambulatory period, 14 days of bed rest, and a 4-day recovery period. During bed rest, dietary intake was supplemented with either 30 mmol/day each of glycine, serine, and alanine (group 1) or with 30 mmol/day each of the three BCAAs (group 2). Whole body protein synthesis was determined with U-(15)N-labeled amino acids, muscle, and selected plasma protein synthesis with l-[(2)H(5)]phenylalanine. Total glucose production and gluconeogenesis from alanine were determined with l-[U-(13)C(3)]alanine and [6,6-(2)H(2)]glucose. During bed rest, nitrogen (N) retention was greater with BCAA feeding (56 +/- 6 vs. 26 +/- 12 mg N. kg(-1). day(-1), P < 0.05). There was no effect of BCAA supplementation on either whole body, muscle, or plasma protein synthesis or the rate of 3-MeH excretion. Muscle tissue free amino acid concentrations were increased during bed rest with BCAA (0.214 +/- 0.066 vs. 0.088 +/- 0.12 nmol/mg protein, P < 0.05). Total glucose production and gluconeogenesis from alanine were unchanged with bed rest but were significantly reduced (P < 0.05) with the BCAA group in the recovery phase. In conclusion, the improved N retention during bed rest is due, at least in part, to accretion of amino acids in the tissue free amino acid pools. The amount accreted is not enough to impact protein kinetics in the recovery phase but does improve N retention by providing additional essential amino acids in the early recovery phase.

Aminoacyl-tRNA and tissue free amino acid pools are equilibrated after a flooding dose of phenylalanine.

The flooding dose method, which is used to measure tissue protein synthesis, assumes equilibration of the isotopic labeling between the aminoacyl-tRNA pool and the tissue and blood free amino acid pools. However, this has not been verified for a phenylalanine tracer in an in vivo study. We determined the specific radioactivity of [(3)H]phenylalanine in the aminoacyl-tRNA and the tissue and blood free amino acid pools of skeletal muscle and liver 30 min after administration of a flooding dose of phenylalanine along with [(3)H]phenylalanine. Studies were performed in neonatal pigs in the fasted and refed states and during hyperinsulinemic-euglycemic-amino acid clamps. The results showed that, 30 min after the administration of a flooding dose of phenylalanine, there was equilibration of the specific radioactivity of phenylalanine among the blood, tissue, and tRNA precursor pools. Equilibration of the specific radioactivity of the three precursor pools for protein synthesis occurred in both skeletal muscle and liver. Neither feeding nor insulin status affected the aminoacyl-tRNA specific radioactivity relative to the tissue free amino acid specific radioactivity. The results support the assumption that the tissue free amino acid pool specific radioactivity is a valid measure of the precursor pool specific radioactivity and thus can be used to calculate protein synthesis rates in skeletal muscle and liver when a flooding dose of phenylalanine is administered.

Hind leg muscle amino acid balances in cold-exposed rats.

The changes in hind leg tissue (muscle and skin) amino acid pool size and arteriovenous balance were measured in rats subjected to 0-90 min of cold exposure (4 degrees C). Tissue free amino acid pools presented a different composition pattern from protein amino acids. Muscle rapidly reacted to cold exposure by releasing small amounts of some amino acids (alanine, aspartate), with only small changes in pool size during the first 30 min. Amino acid oxidation was very limited during the whole period of cold exposure, since at all times tested there was either nil ammonia efflux or net absorption of ammonia and glutamine; i.e. the muscle was in positive nitrogen balance throughout the period studied. Thus most of the amino acid nitrogen taken up from the blood and not found in the free amino acid pools must have been incorporated into protein, since it was not oxidized, as shown by the glutamine and ammonia balance. The data on amino acid incorporation into proteins indicate that hind leg protein turnover is rapidly and widely modulated from a low initial setting upon cold exposure to a higher protein synthesis rate immediately afterwards, suggesting that protein turnover may have an important role in short-term events in cold-exposed muscle, in addition to its influence in long-term adaptation.

A survey of blood and tissue nitrogen compounds in terrestrial decapods of Palau

AbstractTerrestrial decapods have significant levels of ammonia, uric acid and free amino acids in their blood, but blood is hypo‐osmotic to local seawater by as much as 300 mOsm/kg. Blood water content is approximately 90%, with protein making up virtually all the difference, whereas tissue water is between 70% and 80%. The tissue free amino acid pool is composed primarily of glycine, serine, proline, alanine and arginine, which are typical of all crustaceans. The size of the muscle pool is reduced in comparison to aquatic species, while that of gill is comparable. Tissue ammonia levels are very low in comparison to FAA, but these levels are significantly higher in gill than in muscle.

Free Amino Acids in Blood of Ruminants—Physiological and Nutritional Regulation

Tissue free amino acid pools account for only a small fraction of the total amino acid content in the body. Blood of plasma free amino acid pools represent only a very small proportion of tissue free amino pools. Plasma free amino acid profiles have been used as a tool to study nutritional and metabolic aspects of protein status. Static measurements of plasma amino acid levels have limited value as sensitive indicators of protein status because such measurements do not reflect the magnitude of amino acid fluxes in and out free amino acid pools. Use of plasma amino acid profiles, under well defined experimental conditions, in assessing limiting amino acids and essential amino acid requirements in ruminants is discussed.

Ingestion and assimilation of dissolved amino acids by a starfish

1. 1. Levels of free amino acids were measured in the digestive glands of groups of the Tampa Bay starfish. Echinaster, for 10 days following their ingestion of a dissolved amino acid mixture (casein hydrolysate). Similar measurements were made on unfed controls. 2. 2. Ingestion produced a significant elevation of the tissue free amino acid pool level to over twice the control level. This increase mostly represented an accumulation and concentration of the specific ingested amino acids to levels generally 20–50 times above those of the initial medium. The elevated levels diminished only slowly, and were still significant after 48 hr. 3. 3. The prolonged elevation of digestive gland amino acid pools following feeding may be expected to enhance coelomic translocation of amino acids to other body regions. 4. 4. Glycine and taurine levels, always high. did not change significantly with the ingestion. Some decline in glycine levels in unfed controls suggests metabolic utilization of this metabolite with starvation.

Comparison of turnover rates of proteins of the brain, liver and kidney in mouse in vivo following long term labeling

Intraperitoneal injection of [ 14C] tyrosine suspension followed by subcutaneous implantation of a [ 14C] tyrosine pellet in mice produced a fairly constant specific activity of plasma free tyrosine for 5 days, and for 3–5 days in the tissue free amino acid pool. The specific activity of tyrosine in the tissue (brain, liver, and kidney) free amino acid pool was 75–90% of that in plasma. Incorporation of tyrosine into tissue proteins was followed for 5 days in brain; during this time 33% of tissue proteins were labeled. Incorporation for 68 h in liver and kidney showed labeling of over 70% of the protein of these tissues. These percentages assume a homogeneous tissue free tyrosine pool as the precursor. The rate of incorporation initially was 0.6, 2.8, and 2.0% per h in brain, liver, and kidney protein, respectively. These rates decreased in longer term experiments. The best fit to the incorporation curves was obtained by assuming the following average half-lives for tissue proteins: brain, two compartments, 5.7% with a half-life of 15 h, 94.3% with a half-life of 10 days; liver, a single compartment with a 26-h half-life; kidney, two compartments, 41% with an 18-h half-life, and 59% with a 63-h half-life.

Relationship between ammonia excretion rates and hemolymph nitrogenous compounds of a euryhaline bivalve during low salinity acclimation.

1. Free amino acid concentrations in the hemolymph increase rapidly in company with a decrease in the tissue free amino acid pool of propped-open M. demissus exposed to low salinity.2. As acclimation proceeds, blood amino acid concentrations level off and an increase in both hemolymph ammonia concentration and external ammonia excretion occurs.3. Finally, hemolymph amino acid concentrations decrease toward control levels, followed by hemolymph ammonia concentration and external ammonia excretion rates.4. Following complete acclimation of mussels to high or low salinity, ammonia excretion rates are the same. However, hemolymph free amino acid concentrations are lower in animals adapted to low salinity.5. These results show that during acclimation of mussels to low salinity, free amino acids are released intact from the cells into the hemolymph. The subsequent transitory increase in hemolymph ammonia concentrations and external ammonia excretion rates is probably due to degradation of the effluxed amino aci...

The specific radioactivity of the tissue free amino acid pool as a basis for measuring the rate of protein synthesis in the rat in vivo.

1. Rats were infused in vivo with [U-(14)C]glycine for periods of 2-6h, during which time the specific radioactivity of the free glycine in plasma and tissue approached a constant value. 2. Free serine also became labelled. The ratio of specific radioactivity of serine to that of glycine in the protein of liver, kidney, brain, jejunum, heart, diaphragm and gastrocnemius muscle was closer to the ratio in the free amino acid pool of the tissue than that of the plasma. 3. The kinetics of incorporation of [(14)C]glycine and [(14)C]serine into the protein of gastrocnemius muscle further suggested that the plasma free amino acids were not the immediate precursors of protein. 4. Infusion of rats with [U-(14)C]serine resulted in labelling of free glycine. The ratio of specific radioactivity of glycine to serine in the protein of liver, kidney, brain, jejunum and heart again suggested incorporation from a pool similar to the free amino acid pool of the tissue. 5. Rates of tissue protein synthesis calculated from the incorporation into protein of both radioactive glycine and serine, either infused or derived, were very similar when the precursor specific radioactivity was taken to be that in the total free amino acids of the tissue. Except for gastrocnemius muscle and diaphragm during the infusion of radioactive serine, the rates of tissue protein synthesis calculated from the specific radioactivity of the free glycine and serine in plasma differed markedly.