scholarly journals Amino acid regulation of synthesis of ribonucleic acid and protein in the liver of rats

1971 ◽  
Vol 124 (2) ◽  
pp. 385-392 ◽  
Author(s):  
R. W. Wannemacher ◽  
C. F. Wannemacher ◽  
M. B. Yatvin
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Free Amino Acids ◽  
Free Amino ◽  
Cellular Protein ◽  
Deficient Diet ◽  
Cellular Protein Content ◽  
Regulate Protein

Weanling (23-day-old) rats were fed on either a low-protein diet (6% casein) or a diet containing an adequate amount of protein (18% casein) for 28 days. Hepatic cells from animals fed on the deficient diet were characterized by markedly lower concentrations of protein and RNA in all cellular fractions as compared with cells from control rats. The bound rRNA fraction was decreased to the greatest degree, whereas the free ribosomal concentrations were only slightly less than in control animals. A good correlation was observed between the rate of hepatic protein synthesis in vivo and the cellular protein content of the liver. Rates of protein synthesis both in vivo and in vitro were directly correlated with the hepatic concentration of individual free amino acids that are essential for protein synthesis. The decreased protein-synthetic ability of the ribosomes from the liver of protein-deprived rats was related to a decrease in the number of active ribosomes and heavy polyribosomes. The lower ribosomal content of the hepatocytes was correlated with the decreased concentration of essential free amino acids. In the protein-deprived rats, the rate of accumulation of newly synthesized cytoplasmic rRNA was markedly decreased compared with control animals. From these results it was concluded that amino acids regulate protein synthesis (1) by affecting the number of ribosomes that actively synthesize protein and (2) by inhibiting the rate of synthesis of new ribosomes. Both of these processes may involve the synthesis of proteins with a rapid rate of turnover.

Correlation between osmoregulation and cell volume regulation

1987 ◽  
Vol 252 (4) ◽  
pp. R768-R773
Author(s):  
M. A. Lang
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Osmotic Pressure ◽  
Cell Volume ◽  
Free Amino Acids ◽  
Volume Regulation ◽  
Free Amino ◽  
Cell Volume Regulation

The euryhaline crab, Callinectes sapidus, behaves both as an osmoregulator when equilibrated in salines in the range of 800 mosM and below and an osmoconformer when equilibrated in salines above 800 mosM. There exists a close correlation between osmoregulation seen in the whole animal in vivo and cell volume regulation studied in vitro. Hyperregulation of the hemolymph osmotic pressure and cell volume regulation both occurred in salines at approximately 800 mosM and below. During long-term equilibration of the crabs to a wide range of saline environments, the total concentration of hemolymph amino acids plus taurine remained below 3 mM. During the first 6 h after an acute osmotic stress to the whole animal, the hemolymph osmotic pressure and Na activity gradually decreased, whereas the free amino acids remained below 3 mM. As the hemolymph osmotic pressure decreased below approximately 850 mosM, the amino acid level began to increase to 17-25 mM. This change was primarily due to increases in glycine, proline, taurine, and alanine. The likely source of the increase in hemolymph free amino acids in vivo is the free amino acid loss from muscle cells observed during cell volume regulation in vitro.

scholarly journals Pinocytosis and intracellular degradation of exogenous protein: modulation by amino acids.

1983 ◽  
Vol 96 (6) ◽  
pp. 1586-1591 ◽  
Author(s):  
J M Besterman ◽  
J A Airhart ◽  
R B Low ◽  
D E Rannels
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Free Amino Acids ◽  
Free Amino ◽  
De Novo ◽  
Serum Proteins ◽  
Fluid Phase ◽  
Cellular Protein ◽  
Intracellular Degradation ◽  
Exogenous Protein

Intracellular degradation of exogenous (serum) proteins provides a source of amino acids for cellular protein synthesis. Pinocytosis serves as the mechanism for delivering exogenous protein to the lysosomes, the major site of intracellular degradation of exogenous protein. To determine whether the availability of extracellular free amino acids altered pinocytic function, we incubated monolayers of pulmonary alveolar macrophages with the fluid-phase marker, [14C]sucrose, and we dissected the pinocytic process by kinetic analysis. Additionally, intracellular degradation of endogenous and exogenous protein was monitored by measuring phenylalanine released from the cell monolayers in the presence of cycloheximide. Results revealed that in response to a subphysiological level of essential amino acids or to amino acid deprivation, (a) the rate of fluid-phase pinocytosis increased in such a manner as to preferentially increase both delivery to and size of an intracellular compartment believed to be the lysosomes, (b) the degradation of exogenously supplied albumin increased, and (c) the fraction of phenylalanine derived from degradation of exogenous albumin and reutilized for de novo protein synthesis increased. Thus, modulation of the pinosome-lysosome pathway may represent a homeostatic mechanism sensitive to the availability of extracellular free amino acids.

Effects in vivo and in vitro of l-glutamic acid-γ-hydrazide on metabolism of some free amino acids in brain and liver

1966 ◽  
Vol 15 (11) ◽  
pp. 1831-1845 ◽  
Author(s):  
Ricardo Tapia ◽  
Herminia Pasantes ◽  
Berta G. Ortega ◽  
Guillermo H. Massieu
Keyword(s):  
Amino Acids ◽  
Glutamic Acid ◽  
Free Amino Acids ◽  
Free Amino

Absorption of two Tripeptides by the Human Small Intestine: A Study Using a Perfusion Technique

1974 ◽  
Vol 46 (3) ◽  
pp. 393-402 ◽  
Author(s):  
D. B. A. Silk ◽  
D. Perrett ◽  
Joan P. W. Webb ◽  
M. L. Clark
Keyword(s):  
Amino Acids ◽  
Free Amino Acids ◽  
Free Amino ◽  
Acid Mixture ◽  
Mucosal Cell ◽  
Perfusion Technique ◽  
Glycine Solution ◽  
Glycyl Glycine

1. A double-lumen perfusion technique has been used in man to study intestinal absorption of two tripeptides, glycyl-glycyl-glycine and l-alanyl-glycyl-glycine. Intraluminal tripeptide hydrolysis has been investigated by incubating both tripeptides in vitro with fresh uncentrifuged saline aspirates. 2. Glycine was absorbed faster from a glycyl-glycyl-glycine solution (3·3 mmol/l) than from an equivalent (10 mmol/l) glycine solution, and both l-alanine and glycine were absorbed faster from 10 mmol/l l-alanyl-glycyl-glycine than from the equivalent amino acid mixture. Free amino acids and dipeptides were aspirated during the tripeptide perfusions. 3. l-Alanyl-glycyl-glycine was hydrolysed faster than glycyl-glycyl-glycine in vitro, and results indicated that hydrolysis of the tripeptides occurred from the N-terminal end of the molecule. Intraluminal tripeptide hydrolysis was not sufficient to account for the concentrations of free amino acids and dipeptides liberated during the tripeptide perfusion experiments in vivo. 4. It is suggested that the liberated amino acids and dipeptides either diffused back into the luminal contents after hydrolysis in the brush border had taken place, or effluxed from the mucosal cell after intracellular tripeptide hydrolysis.

ACTION OF THYROTROPHIN (TSH) ON THYROID PROTEIN SYNTHESIS IN VIVO AND IN VITRO

1973 ◽  
Vol 72 (3) ◽  
pp. 453-463 ◽  
Author(s):  
Gustav Wägar ◽  
Ragnar Ekholm ◽  
Ulla Björkman
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Free Amino ◽  
Microsomal Fraction ◽  
Inhibitory Effect ◽  
Leucine Incorporation ◽  
Bovine Thyroid ◽  
Stimulation Of

ABSTRACT The effect of TSH on the incorporation of L-14C-leucine into thyroid proteins was studied in vivo in rats as well as in vitro on bovine thyroid slices and a microsomal subfraction. It was found that TSH reduced the incorporation of radio-leucine into the proteins of slices during the first 2 hours when the concentration of non-labelled leucine in the incubation medium was low. When cold leucine was added to the medium this inhibitory effect was no longer observed. After 6 hours a stimulatory effect on the radio-leucine incorporation by TSH was obvious at both low and high leucine concentrations. The incorporation of 14C-leucine into proteins by the microsomal fraction incubated with a pH 5-fraction was reduced by TSH but this inhibitory effect of TSH disapperaed when post-microsomal supernatant, containing free amino acids, was added to the incubation mixture. It is suggested that the apparent inhibitory effect of TSH on protein synthesis in thyroid slices is due to an altered ratio labelled/non-labelled leucine, caused by stimulation of proteolysis by TSH. This explanation does not seem applicable, however, to the similar apparently inhibitory effect of TSH on protein synthesis observed in the microsomal fraction. In the in vivo experiments a stimulation of the incorporation of labelled leucine could not be observed until 4 hours after the TSH administration. It is suggested that this apparently slow effect of TSH on protein synthesis might be explained either by an indirect effect of TSH on protein synthesis or by a TSH-induced change of the ratio labelled/non-labelled leucine.

scholarly journals Disturbance in hemoglobin metabolism and in vivo antimalarial activity of azole antimycotics

2011 ◽  
Vol 53 (1) ◽  
pp. 25-29 ◽  
Author(s):  
Juan Ricardo Rodrigues ◽  
Diana Lourenco ◽  
Neira Gamboa
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Post Infection ◽  
Free Amino ◽  
Antimalarial Activity ◽  
Sds Page ◽  
Ic50 Values ◽  
Hemoglobin Metabolism

Plasmodium parasites degrade host hemoglobin to obtain free amino acids, essential for protein synthesis. During this event, free toxic heme moieties crystallize spontaneously to produce a non-toxic pigment called hemozoin or ß-hematin. In this context, a group of azole antimycotics, clotrimazole (CTZ), ketoconazole (KTZ) and fluconazole (FCZ), were investigated for their abilities to inhibit ß-hematin synthesis (IßHS) and hemoglobin proteolysis (IHbP) in vitro. The ß-hematin synthesis was recorded by spectrophotometry at 405 nm and the hemoglobin proteolysis was determined by SDS-PAGE 12.5%, followed by densitometric analysis. Compounds were also assayed in vivo in a malaria murine model. CTZ and KTZ exhibited the maximal effects inhibiting both biochemical events, showing inhibition of β-hematin synthesis (IC50 values of 12.4 ± 0.9 µM and 14.4 ± 1.4 µM respectively) and inhibition of hemoglobin proteolysis (80.1 ± 2.0% and 55.3 ± 3.6%, respectively). There is a broad correlation to the in vivo results, especially CTZ, which reduced the parasitemia (%P) of infected-mice at 4th day post-infection significantly compared to non-treated controls (12.4 ± 3.0% compared to 26.6 ± 3.7%, p = 0.014) and prolonged the survival days post-infection. The results indicated that the inhibition of the hemoglobin metabolism by the azole antimycotics could be responsible for their antimalarial effect.

Turnover of total proteins and ornithine aminotransferase during liver regeneration in rats

1980 ◽  
Vol 238 (1) ◽  
pp. E46-E52
Author(s):  
S. L. Augustine ◽  
R. W. Swick
Keyword(s):  
Amino Acids ◽  
Liver Regeneration ◽  
Protein Degradation ◽  
Partial Hepatectomy ◽  
Free Amino ◽  
Liver Protein ◽  
Ornithine Aminotransferase ◽  
Fractional Rate

The recovery of approximately 40% of the total liver protein during the first day after partial hepatectomy was shown to be due to the near cessation of protein breakdown rather than to an increase in protein synthesis. The decrease in degradation of total protein was less if rats were adrenalectomized or protein-depleted prior to partial hepatectomy. The effect of these treatments originally suggested that changes in free amino acid levels in liver might be related to the rate of protein degradation. However, no correlation was found between levels of total free amino acids and rates of breakdown. Measurements of individual amino acids during liver regeneration suggested that levels of free methionine and phenylalanine, amino acids that have been found to lower rates of protein degradation in vitro, are not correlated with rates of breakdown in vivo. The difference between the fractional rate of ornithine aminotransferase degradation (0.68/day and 0.28/day in sham-hepatectomized and partially hepatectomized rats, respectively) was sufficient to account for the higher level of this protein 3 days after surgery in the latter group.

Effect of Cycloheximide on In Vitro and In Vivo Protein Synthesis by Certain Tissues of Rats and Pigeons with Special Reference to Muscle

1973 ◽  
Vol 51 (12) ◽  
pp. 933-941 ◽  
Author(s):  
Njanoor Narayanan ◽  
Jacob Eapen
Keyword(s):  
Amino Acids ◽  
Body Weight ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Amino Acid Incorporation ◽  
Contrast Administration ◽  
Acid Incorporation ◽  
Tissue Homogenates

The effect of cycloheximide in vitro and in vivo on the incorporation of labelled amino acids into protein by muscles, liver, kidneys, and brain of rats and pigeons was studied. In vitro incorporation of amino acids into protein by muscle microsomes, myofibrils, and myofibrillar ribosomes was not affected by cycloheximide. In contrast, administration of the antibiotic into intact animals at a concentration of 1 mg/kg body weight resulted in considerable inhibition of amino acid incorporation into protein by muscles, liver, kidneys, and brain. This inhibition was observed in all the subcellular fractions of these tissues during a period of 10–40 min after the administration of the precursor. Tissue homogenates derived from in vivo cycloheximide-treated animals did not show significant alteration in in vitro amino acid incorporation with the exception of brain, which showed a small but significant enhancement.

scholarly journals The rate-limiting step of protein synthesis in vivo and in vitro and the distribution of growing peptides between the puromycinlabile and puromycin-non-labile sites on polyribosomes

1971 ◽  
Vol 122 (3) ◽  
pp. 267-276 ◽  
Author(s):  
D. C. N. Earl ◽  
Susan T. Hindley
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Donor Site ◽  
Peptide Bond ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Donor And Acceptor ◽  
Rate Limiting

1. At 3 min after an intravenous injection of radioactive amino acids into the rat, the bulk of radioactivity associated with liver polyribosomes can be interpreted as growing peptides. 2. In an attempt to identify the rate-limiting step of protein synthesis in vivo and in vitro, use was made of the action of puromycin at 0°C, in releasing growing peptides only from the donor site, to study the distribution of growing peptides between the donor and acceptor sites. 3. Evidence is presented that all growing peptides in a population of liver polyribosomes labelled in vivo are similarly distributed between the donor and acceptor sites, and that the proportion released by puromycin is not an artifact of methodology. 4. The proportion released by puromycin is about 50% for both liver and muscle polyribosomes labelled in vivo, suggesting that neither the availability nor binding of aminoacyl-tRNA nor peptide bond synthesis nor translocation can limit the rate of protein synthesis in vivo. Attempts to alter this by starvation, hypophysectomy, growth hormone, alloxan, insulin and partial hepatectomy were unsuccessful. 5. Growing peptides on liver polyribosomes labelled in a cell-free system in vitro or by incubating hemidiaphragms in vitro were largely in the donor site, suggesting that either the availability or binding of aminoacyl-tRNA, or peptide bond synthesis, must be rate limiting in vitro and that the rate-limiting step differs from that in vivo. 6. Neither in vivo nor in the hemidiaphragm system in vitro was a correlation found between the proportion of growing peptides in the donor site and changes in the rate of incorporation of radioactivity into protein. This could indicate that the intracellular concentration of amino acids or aminoacyl-tRNA limits the rate of protein synthesis and that the increased incorporation results from a rise to a higher but still suboptimum concentration.

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