scholarly journals Pools and protein synthesis in mammalian cells

1979 ◽  
Vol 178 (3) ◽  
pp. 699-709 ◽  
Author(s):  
J H Robertson ◽  
D N Wheatley
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Mammalian Cells ◽  
External Medium ◽  
Essential Amino Acids ◽  
Poor Correlation ◽  
Experimental Conditions ◽  
Linear Kinetics ◽  
Kinetics Of

From the kinetics of incorporation into protein shown by four amino acids and one amino acid analogue in suspension cultured HeLa S-3 cells, two distinctly different patterns were observed under the same experimental conditions. An initial slow exponential incorporation followed by linear kinetics was characteristic of the two non-essential amino acids, glycine and proline, whereas the two essential amino acids studied, phenylalanine and leucine, showed linear kinetics of incorporation with no detectable delay. The analogue amino acid, p-fluorophenylalanine also showed immediate linear kinetics of incorporation. There was a poor correlation between the rate of formation of acid-soluble pools and incorporation kinetics. However, the rate of formation of the freely diffusible pool of amino acids correlated more closely with incorporation kinetics. The lack of direct involvement of the acid-soluble pool in protein synthesis was also demonstrated by pre-loading of pools before treatment of cells with labelled amino acids. The results partially support the hypothesis that precursor amino acids for protein synthesis come from the external medium rather than the acid-soluble pool, but suggest that the amino acid which freely diffuses into the cell from the external medium could also be the source.

scholarly journals Identification in skeletal muscle of a distinct extracellular pool of amino acids, and its role in protein synthesis

1971 ◽  
Vol 121 (5) ◽  
pp. 817-827 ◽  
Author(s):  
R. C. Hider ◽  
E. B. Fern ◽  
D. R. London
Keyword(s):  
Skeletal Muscle ◽  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Incubation Medium ◽  
Extensor Digitorum Longus ◽  
Extensor Digitorum ◽  
Longus Muscle ◽  
Kinetics Of

1. The kinetics of radioactive labelling of extra- and intra-cellular amino acid pools and protein of the extensor digitorum longus muscle were studied after incubations with radioactive amino acids in vitro. 2. The results indicated that an extracellular pool could be defined, the contents of which were different from those of the incubation medium. 3. It was concluded that amino acids from the extracellular pool, as defined in this study, were incorporated directly into protein.

Meal stimulation of albumin synthesis: a significant contributor to whole body protein synthesis in humans

1992 ◽  
Vol 263 (4) ◽  
pp. E794-E799 ◽  
Author(s):  
P. De Feo ◽  
F. F. Horber ◽  
M. W. Haymond
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Combined Treatment ◽  
Essential Amino Acids ◽  
Whole Body ◽  
Albumin Synthesis ◽  
Body Protein ◽  
Peripheral Tissues ◽  
Stimulation Of

The present studies were performed to test the hypothesis that the liver, by increasing the synthesis of specific plasma proteins during the absorption of an amino acid meal, may play an important role in the temporary "storage" of ingested essential amino acids and to explore the effects of glucocorticosteroids and recombinant human growth hormone (rhGH) on these processes. The fractional synthetic rates of albumin and fibrinogen were determined using simultaneous infusions of intravenous [1-14C]leucine and intraduodenal [4,5-3H]leucine after 22 h fasting and during absorption of glucose and amino acids in four groups of normal subjects treated for 1 wk with placebo, prednisone (0.8 mg.kg-1.day-1), rhGH (0.1 mg.kg-1.day-1), or combined treatment. When compared with the fasted state and independent of the route of tracer delivery and hormonal treatment, albumin, but not fibrinogen, synthesis increased (P < 0.0001) during absorption of a mixed glucose amino acid meal in all groups. This increase in albumin synthesis accounted for 28% of the increase in whole body protein synthesis associated with feeding and for 24, 22, and 14% in the prednisone, rhGH, and combined treatment groups, respectively. These data suggest that the stimulation of albumin synthesis observed during feeding prevents irreversible oxidative losses of a significant fraction of ingested essential amino acids and may serve as a vehicle to capture excess dietary amino acids and transport them to peripheral tissues to sustain local protein synthesis.

scholarly journals The Role of the Anabolic Properties of Plant- versus Animal-Based Protein Sources in Supporting Muscle Mass Maintenance: A Critical Review

Nutrients ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1825 ◽  
Author(s):  
Insaf Berrazaga ◽  
Valérie Micard ◽  
Marine Gueugneau ◽  
Stéphane Walrand
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Amino Acid Composition ◽  
Protein Intake ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Essential Amino Acids ◽  
Protein Sources ◽  
Nutritional Strategies

Plant-sourced proteins offer environmental and health benefits, and research increasingly includes them in study formulas. However, plant-based proteins have less of an anabolic effect than animal proteins due to their lower digestibility, lower essential amino acid content (especially leucine), and deficiency in other essential amino acids, such as sulfur amino acids or lysine. Thus, plant amino acids are directed toward oxidation rather than used for muscle protein synthesis. In this review, we evaluate the ability of plant- versus animal-based proteins to help maintain skeletal muscle mass in healthy and especially older people and examine different nutritional strategies for improving the anabolic properties of plant-based proteins. Among these strategies, increasing protein intake has led to a positive acute postprandial muscle protein synthesis response and even positive long-term improvement in lean mass. Increasing the quality of protein intake by improving amino acid composition could also compensate for the lower anabolic potential of plant-based proteins. We evaluated and discussed four nutritional strategies for improving the amino acid composition of plant-based proteins: fortifying plant-based proteins with specific essential amino acids, selective breeding, blending several plant protein sources, and blending plant with animal-based protein sources. These nutritional approaches need to be profoundly examined in older individuals in order to optimize protein intake for this population who require a high-quality food protein intake to mitigate age-related muscle loss.

scholarly journals Postexercise net protein synthesis in human muscle from orally administered amino acids

1999 ◽  
Vol 276 (4) ◽  
pp. E628-E634 ◽  
Author(s):  
Kevin D. Tipton ◽  
Arny A. Ferrando ◽  
Stuart M. Phillips ◽  
David Doyle ◽  
Robert R. Wolfe
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Resistance Exercise ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Random Order ◽  
Essential Amino Acids ◽  
Constant Infusion ◽  
Protein Balance

We examined the response of net muscle protein synthesis to ingestion of amino acids after a bout of resistance exercise. A primed, constant infusion ofl-[ ring-2H5]phenylalanine was used to measure net muscle protein balance in three male and three female volunteers on three occasions. Subjects consumed in random order 1 liter of 1) a mixed amino acid (40 g) solution (MAA), 2) an essential amino acid (40 g) solution (EAA), and 3) a placebo solution (PLA). Arterial amino acid concentrations increased ∼150–640% above baseline during ingestion of MAA and EAA. Net muscle protein balance was significantly increased from negative during PLA ingestion (−50 ± 23 nmol ⋅ min−1 ⋅ 100 ml leg volume−1) to positive during MAA ingestion (17 ± 13 nmol ⋅ min−1 ⋅ 100 ml leg volume−1) and EAA (29 ± 14 nmol ⋅ min−1 ⋅ 100 ml leg volume−1; P < 0.05). Because net balance was similar for MAA and EAA, it does not appear necessary to include nonessential amino acids in a formulation designed to elicit an anabolic response from muscle after exercise. We concluded that ingestion of oral essential amino acids results in a change from net muscle protein degradation to net muscle protein synthesis after heavy resistance exercise in humans similar to that seen when the amino acids were infused.

Effects of increased supply of essential amino acids on the metabolism of the isolated perfused guinea-pig mammary gland

1979 ◽  
Vol 46 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Andrew R. Peters ◽  
Stephen Alexandrov ◽  
T. Ben Mepham
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Mammary Gland ◽  
Amino Acid ◽  
Guinea Pig ◽  
Amino Acid Uptake ◽  
Essential Amino Acids ◽  
Acid Uptake ◽  
Isoleucine Leucine ◽  
Group 1

SUMMARYThe effects of high rates of infusion of essential amino acids on amino acid uptake by the isolated perfused guinea-pig mammary gland were studied. Infusion of methionine, tyrosine, phenylalanine, histidine and tryptophan (designated group 1) resulted in significant increases in the uptakes of tyrosine, phenylalanine and histidine. Methionine, tryptophan and other essential amino acids were not significantly affected. Infusion of threonine, valine, isoleucine, leucine, lysine and arginine (designated group 2) resulted in significant increases in uptake of all these amino acids. Group 1 amino acid uptake was not significantly affected. Infusion of all the essential amino acids (i.e. groups 1 and 2 together) resulted in significant increases in all their uptakes. Using as index ‘the predicted rate of protein synthesis’, infusion of group 1 and 2 together led to an apparent 27% increase in protein synthesis. The above results are discussed in relation to the control of milk protein synthesis by limiting essential amino acids.

scholarly journals Role of specific dietary amino acids in clinical conditions

2012 ◽  
Vol 108 (S2) ◽  
pp. S139-S148 ◽  
Author(s):  
Renate Jonker ◽  
Mariëlle P. K. J. Engelen ◽  
Nicolaas E. P. Deutz
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Wasting ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Essential Amino Acids ◽  
Dietary Proteins ◽  
Disease States ◽  
Stimulation Of

In a variety of chronic and acute disease states, alterations in protein synthesis, breakdown and protein turnover rates occur that are related to the loss of body protein and skeletal muscle wasting. A key observation is the stimulation of protein breakdown in muscle and the stimulation of protein synthesis in the splanchnic area; mainly liver. An altered splanchnic extraction of amino acids as well as an anabolic resistance to dietary protein, related to stress, disuse and aging play a key role in the pathogenesis of muscle wasting in these conditions. To overcome these factors, specific dietary protein and amino acid diets have been introduced. The main focus of these diets is the quantity and quality of dietary proteins and whether a balanced mixture or solely dietary essential amino acids are required with or without higher intake levels of specific amino acids. Specifically in cancer patients, stimulated muscle protein synthesis has been obtained by increasing the amount of protein in a meal and by providing additional leucine. Also in other chronic diseases such as chronic obstructive pulmonary disease and cystic fibrosis, meals with specific dietary proteins and specific combinations of dietary essential amino acids are able to stimulate anabolism. In acute diseases, a special role for the amino acid arginine and its precursor citrulline as anabolic drivers has been observed. Thus, there is growing evidence that modifying the dietary amino acid composition of a meal will positively influence the net balance between muscle protein synthesis and breakdown, leading to muscle protein anabolism in a variety of chronic and acute disease states. Specific amino acids with anabolic potential are leucine, arginine and citrulline.

scholarly journals Amino acid homeostasis and signalling in mammalian cells and organisms

2017 ◽  
Vol 474 (12) ◽  
pp. 1935-1963 ◽  
Author(s):  
Stefan Bröer ◽  
Angelika Bröer
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Food Intake ◽  
Essential Amino Acids ◽  
Acid Oxidation ◽  
Plasma Amino Acids ◽  
Amino Acid Oxidation ◽  
Amino Acid Levels ◽  
Amino Acid Depletion

Cells have a constant turnover of proteins that recycle most amino acids over time. Net loss is mainly due to amino acid oxidation. Homeostasis is achieved through exchange of essential amino acids with non-essential amino acids and the transfer of amino groups from oxidised amino acids to amino acid biosynthesis. This homeostatic condition is maintained through an active mTORC1 complex. Under amino acid depletion, mTORC1 is inactivated. This increases the breakdown of cellular proteins through autophagy and reduces protein biosynthesis. The general control non-derepressable 2/ATF4 pathway may be activated in addition, resulting in transcription of genes involved in amino acid transport and biosynthesis of non-essential amino acids. Metabolism is autoregulated to minimise oxidation of amino acids. Systemic amino acid levels are also tightly regulated. Food intake briefly increases plasma amino acid levels, which stimulates insulin release and mTOR-dependent protein synthesis in muscle. Excess amino acids are oxidised, resulting in increased urea production. Short-term fasting does not result in depletion of plasma amino acids due to reduced protein synthesis and the onset of autophagy. Owing to the fact that half of all amino acids are essential, reduction in protein synthesis and amino acid oxidation are the only two measures to reduce amino acid demand. Long-term malnutrition causes depletion of plasma amino acids. The CNS appears to generate a protein-specific response upon amino acid depletion, resulting in avoidance of an inadequate diet. High protein levels, in contrast, contribute together with other nutrients to a reduction in food intake.

Effects of Amino Acid Intake on Anabolic Processes

2001 ◽  
Vol 26 (S1) ◽  
pp. S220-S227 ◽  
Author(s):  
Robert R. Wolfe
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Essential Amino Acids ◽  
Negative Resistance ◽  
Static Concentration ◽  
Amino Acid Intake ◽  
Modest Effect

In the resting state muscle protein breakdown exceeds the rate of muscle protein synthesis, meaning that the balance between synthesis and breakdown is negative. Resistance exercise improves the net balance by stimulating muscle protein synthesis, but nutrient intake is requiredfor synthesis to exceed breakdown (i.e., an anabolic response). Exercise and exogenous amino acids have an additive effect on muscle protein synthesis. There is a timecourse of the response to a steady-state change in amino acid concentration. The signal for stimulation of muscle protein synthesis appears to be the extracellular concentrations of one or more of the essential amino acids (EAAs). Further, the rate , and direction, of change in extracellular concentrations (rather than the static concentration, per se) may be the important. Ingestion of non-essential AAs is not needed to stimulate muscle protein synthesis. Carbohydrate has, at most, a modest effect to enhance the response to amino acid ingestion after exercise. Finally, a mixture of EAAs + CRO more effectively stimulates muscle protein synthesis when taken before as opposed to after exercise.

scholarly journals Initiation of Protein Synthesis in Mammalian Cells with Codons Other Than AUG and Amino Acids Other Than Methionine

1998 ◽  
Vol 18 (9) ◽  
pp. 5140-5147 ◽  
Author(s):  
Harold J. Drabkin ◽  
Uttam L. RajBhandary
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Mammalian Cells ◽  
Initiator Trna ◽  
Cell Extracts ◽  
Potential Applications ◽  
Protein Synthesis Initiation ◽  
Amino Acid Methionine ◽  
The Many

ABSTRACT Protein synthesis is initiated universally with the amino acid methionine. In Escherichia coli, studies with anticodon sequence mutants of the initiator methionine tRNA have shown that protein synthesis can be initiated with several other amino acids. In eukaryotic systems, however, a yeast initiator tRNA aminoacylated with isoleucine was found to be inactive in initiation in mammalian cell extracts. This finding raised the question of whether methionine is the only amino acid capable of initiation of protein synthesis in eukaryotes. In this work, we studied the activities, in initiation, of four different anticodon sequence mutants of human initiator tRNA in mammalian COS1 cells, using reporter genes carrying mutations in the initiation codon that are complementary to the tRNA anticodons. The mutant tRNAs used are aminoacylated with glutamine, methionine, and valine. Our results show that in the presence of the corresponding mutant initiator tRNAs, AGG and GUC can initiate protein synthesis in COS1 cells with methionine and valine, respectively. CAG initiates protein synthesis with glutamine but extremely poorly, whereas UAG could not be used to initiate protein synthesis with glutamine. We discuss the potential applications of the mutant initiator tRNA-dependent initiation of protein synthesis with codons other than AUG for studying the many interesting aspects of protein synthesis initiation in mammalian cells.

scholarly journals An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise

2000 ◽  
Vol 88 (2) ◽  
pp. 386-392 ◽  
Author(s):  
Blake B. Rasmussen ◽  
Kevin D. Tipton ◽  
Sharon L. Miller ◽  
Steven E. Wolf ◽  
Robert R. Wolfe
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Resistance Exercise ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Venous Blood ◽  
Compartment Model ◽  
Essential Amino Acids

This study was designed to determine the response of muscle protein to the bolus ingestion of a drink containing essential amino acids and carbohydrate after resistance exercise. Six subjects (3 men, 3 women) randomly consumed a treatment drink (6 g essential amino acids, 35 g sucrose) or a flavored placebo drink 1 h or 3 h after a bout of resistance exercise on two separate occasions. We used a three-compartment model for determination of leg muscle protein kinetics. The model involves the infusion of ring-2H5-phenylalanine, femoral arterial and venous blood sampling, and muscle biopsies. Phenylalanine net balance and muscle protein synthesis were significantly increased above the predrink and corresponding placebo value ( P < 0.05) when the drink was taken 1 or 3 h after exercise but not when the placebo was ingested at 1 or 3 h. The response to the amino acid-carbohydrate drink produced similar anabolic responses at 1 and 3 h. Muscle protein breakdown did not change in response to the drink. We conclude that essential amino acids with carbohydrates stimulate muscle protein anabolism by increasing muscle protein synthesis when ingested 1 or 3 h after resistance exercise.

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