scholarly journals Protein turnover in pulmonary macrophages Utilization of amino acids derived from protein degradation

1981 ◽  
Vol 198 (1) ◽  
pp. 53-65 ◽  
Author(s):  
J A Hammer ◽  
D E Rannels
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Protein Degradation ◽  
Plasma Concentrations ◽  
Specific Radioactivity ◽  
Pulmonary Macrophages ◽  
Protein Synthesis And Degradation ◽  
Synthesis And Degradation ◽  
Extracellular Amino Acid

Conditions were defined under which rates of protein synthesis and degradation could be estimated in alveolar macrophages isolated from rabbits by pulmonary lavage and incubated in the presence of plasma concentrations of amino acids and 5.6 mM-glucose. Phenylalanine was validated as suitable precursor for use in these studies: it was not metabolized appreciably, except in the pathways of protein synthesis and degradation; it entered the cells rapidly; it maintained a stable intracellular concentration; and it was incorporated into protein at measurable rates. When extracellular phenylalanine was raised to a concentration sufficient to minimize dilution of the specific radioactivity of the precursor for protein synthesis with amino acid derived from protein degradation, the specific radioactivity of phenylalanyl-tRNA was only 60% of that of the extracellular amino acid. This relationship was unchanged in cells where proteolysis increased 2.5-fold after uptake and degradation of exogenous bovine serum albumin. In contrast, albumin prevented the decrease in phenylalanine incorporation observed in macrophages deprived of an exogenous source of amino acids. These observations suggested that macrophages preferentially re-utilized amino acids derived from the degradation of endogenous, but not from exogenous (albumin), protein. However, when the extracellular supply of amino acids was restricted, substrates derived from albumin catabolism could support the protein-synthetic pathway.

scholarly journals Pentoxifylline improves insulin action limiting skeletal muscle catabolism after infection

1999 ◽  
Vol 163 (1) ◽  
pp. 15-24 ◽  
Author(s):  
T Vary ◽  
D Dardevet ◽  
J Grizard ◽  
L Voisin ◽  
C Buffiere ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Protein Degradation ◽  
Muscle Protein ◽  
Plasma Concentrations ◽  
Skeletal Muscle Protein ◽  
Muscle Protein Metabolism ◽  
Protein Synthesis And Degradation ◽  
Synthesis And Degradation

We investigated the ability of pentoxifylline (PTX) to modulate protein synthesis and degradation in the presence and absence of insulin during incubation of epitrochlearis muscle, 2 or 6 days after injection of Escherichia coli. On days 2 and 6 after infection, protein synthesis was inhibited by 25%, whereas proteolysis was enhanced by 75%. Insulin (2 nM) in vitro stimulated protein synthesis in muscles from infected rats to the same extent as in controls. The ability of insulin to limit protein degradation was severely blunted 48 h after infection. On day 6 after infection, insulin inhibited proteolysis to a greater extent than on day 2. PTX suppressed the increase in plasma concentrations of tumor necrosis factor more than 600-fold after injection of bacteria, and partially prevented the inhibition of protein synthesis and stimulation of protein degradation during sepsis. Moreover, PTX administration maintained the responsiveness of protein degradation to insulin during sepsis. Thus cytokines may influence skeletal muscle protein metabolism during sepsis, both indirectly through inhibition of the effects of insulin on proteolysis, and directly on the protein synthesis and degradation machinery.

scholarly journals Reversible inhibition of protein synthesis in lung by halothane

1983 ◽  
Vol 210 (2) ◽  
pp. 379-387 ◽  
Author(s):  
D E Rannels ◽  
R Christopherson ◽  
C A Watkins
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Plasma Concentrations ◽  
Specific Radioactivity ◽  
Bicarbonate Buffer ◽  
Inhibition Of Protein Synthesis ◽  
Glucose Plasma ◽  
Dose Dependent ◽  
Synthesis And Degradation

Alterations in the synthesis and degradation of proteins were investigated in intact lungs exposed to the volatile anaesthetic halothane. In rat lungs perfused in situ with Krebs-Henseleit bicarbonate buffer containing 4.5% (w/v) bovine serum albumin, 5.6 mM-glucose, plasma concentrations of 19 amino acids and 690 microM-[U-14C]-phenylalanine and equilibrated with O2/N2/CO2 (4:15:1), protein synthesis, calculated based on the specific radioactivity of aminoacyl-tRNA, was inhibited by halothane. The anaesthetic did not affect degradation of lung proteins. The inhibition of protein synthesis was rapid in onset, dose-dependent, and quickly reversible. It did not appear to be associated with overall energy depletion, with non-specific changes in cellular permeability, or with decreased availability of amino acids as substrates for protein synthesis.

scholarly journals Measurement of protein synthesis in rat lungs perfused in situ

1980 ◽  
Vol 188 (1) ◽  
pp. 269-278 ◽  
Author(s):  
Clyde A. Watkins ◽  
D. Eugene Rannels
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Free Amino ◽  
Plasma Concentrations ◽  
Specific Radioactivity ◽  
Sole Source ◽  
Bicarbonate Buffer ◽  
Normal Plasma ◽  
Rat Lungs

Compartmentalization of amino acid was investigated to define conditions required for accurate measurements of rates of protein synthesis in rat lungs perfused in situ. Lungs were perfused with Krebs–Henseleit bicarbonate buffer containing 4.5% (w/v) bovine serum albumin, 5.6mm-glucose, normal plasma concentrations of 19 amino acids, and 8.6–690μm-[U-14C]phenylalanine. The perfusate was equilibrated with the same humidified gas mixture used to ventilate the lungs [O2/CO2 (19:1) or O2/N2/CO2 (4:15:1)]. [U-14C]Phenylalanine was shown to be a suitable precursor for studies of protein synthesis in perfused lungs: it entered the tissue rapidly (t½, 81s) and was not converted to other compounds. As perfusate phenylalanine was decreased below 5 times the normal plasma concentration, the specific radioactivity of the pool of phenylalanine serving as precursor for protein synthesis, and thus [14C]phenylalanine incorporation into protein, declined. In contrast, incorporation of [14C]histidine into lung protein was unaffected. At low perfusate phenylalanine concentrations, rates of protein synthesis that were based on the specific radioactivity of phenylalanyl-tRNA were between rates calculated from the specific radioactivity of phenylalanine in the extracellular or intracellular pools. Rates based on the specific radioactivities of these three pools of phenylalanine were the same when extracellular phenylalanine was increased. These observations suggested that: (1) phenylalanine was compartmentalized in lung tissue; (2) neither the extracellular nor the total intracellular pool of phenylalanine served as the sole source of precursor for protein; (3) at low extracellular phenylalanine concentrations, rates of protein synthesis were in error if calculated from the specific radioactivity of the free amino acid; (4) at high extracellular phenylalanine concentrations, the effects of compartmentalization were negligible and protein synthesis could be calculated accurately from the specific radioactivity of the free or tRNA-bound phenylalanine pool.

The Effect of Cell Population Density on Nutrient Uptake and Cell Metabolism: a Comparative Study of Human Diploid and Heteroploid Cell Lines

1972 ◽  
Vol 10 (2) ◽  
pp. 515-524
Author(s):  
J. B. GRIFFITHS
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Dna Synthesis ◽  
Nutrient Uptake ◽  
Cell Lines ◽  
Acid Concentration ◽  
Contact Inhibition ◽  
Inhibition Of Growth ◽  
Extracellular Amino Acid

The possibility that contact inhibition of growth in cultures of human diploid cells is influenced by the effects of cell crowding on nutrient uptake by the cells was investigated. Two human lung cell lines were compared, the diploid line MRC-5 and the heteroploid line L-132. In pre-confluent cultures the ability of these 2 cell types to accumulate amino acids was very similar. Post-confluent L-132 cells showed very little change from the pre-confluent cultures but the ability of MRC-5 cells in post-confluent cultures was greatly reduced. The intracellular concentrations of various amino acids necessary to achieve the maximum rate of protein synthesis were found. These values were identical for sparse and crowded cultures but due to the reduced uptake ability of crowded MRC-5 cells a far higher external amino acid concentration was required in post-confluent cultures. This meant that although amino acids did not become growth-limiting until over 80% utilized in pre-confluent cultures, in post-confluent cultures they became growth-limiting when only 50% utilized. Although protein synthesis was significantly affected by extracellular amino acid concentration and cell crowding, thus contributing towards the effect of contact inhibition of growth, DNA synthesis was shown to be the major metabolic function in contact inhibition. Increased cell density had a very inhibitory effect on DNA synthesis in MRC-5 cultures, but not in L-132 cultures, and this was unaffected by extracellular amino acid and glucose concentration.

Competition for transport of amino acids into rat heart: Effect of competitors on protein synthesis and degradation

Metabolism ◽  
1992 ◽  
Vol 41 (9) ◽  
pp. 925-933 ◽  
Author(s):  
Armando R. Tovar ◽  
Jean K. Tews ◽  
Nimbe Torres ◽  
David C. Madsen ◽  
Alfred E. Harper
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Rat Heart ◽  
Protein Synthesis And Degradation ◽  
Synthesis And Degradation

scholarly journals Comparison of protein synthesis and degradation in incubated and perfused muscle

1983 ◽  
Vol 212 (3) ◽  
pp. 649-653 ◽  
Author(s):  
A S Clark ◽  
W E Mitch
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Insulin Treatment ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Muscle Protein Degradation ◽  
Protein Synthesis And Degradation ◽  
Synthesis And Degradation

Rates of muscle protein synthesis and degradation measured in the perfused hindquarter were compared with those in incubated epitrochlearis muscles. With fed or starved mature rats, results without insulin treatment were identical. With insulin treatment, protein synthesis in perfused hindquarters was greater, though protein degradation was the same. Thus rates of muscle protein degradation estimated by these two methods in vitro correspond closely.

Effects of glucocorticoid treatment on cardiac protein synthesis and degradation

1986 ◽  
Vol 250 (6) ◽  
pp. C821-C827 ◽  
Author(s):  
A. F. Clark ◽  
G. N. DeMartino ◽  
K. Wildenthal
Keyword(s):  
Protein Synthesis ◽  
Protein Degradation ◽  
Lower Body ◽  
Glucocorticoid Treatment ◽  
Body Weights ◽  
Langendorff Perfusion ◽  
Perfused Hearts ◽  
Fasted Rats ◽  
Protein Synthesis And Degradation ◽  
Synthesis And Degradation

We treated rats with dexamethasone (DEX, 1 mg . kg-1 . day-1) and examined the effects of this glucocorticoid on heart protein metabolism using atrial explant and Langendorff perfusion preparations. Fasted rats treated with DEX for 2 days had significantly lower body weights (92% of control, P less than 0.001) and larger hearts (106% of control, P less than 0.005) than fasted control animals. Protein and RNA concentrations remained constant. In atrial explants, DEX treatment produced a 19% increase in protein synthesis (P less than 0.001) and a 13% increase in protein degradation (P less than 0.002). In Langendorff-perfused hearts, DEX treatment caused a 36% increase in protein synthesis (P less than 0.02), while protein degradation was 8% above control (P greater than 0.05). Thus, in contrast to their catabolic effects on skeletal muscle, glucocorticoids are anabolic on the heart. The increased accumulation of total cardiac protein during early glucocorticoid administration is mediated entirely via increased rates of synthesis.

scholarly journals The regulation of protein synthesis in the liver of rats. Mechanisms of dietary amino acid control in the immature animal

1968 ◽  
Vol 107 (5) ◽  
pp. 615-623 ◽  
Author(s):  
R. W. Wannemacher ◽  
W. K. Cooper ◽  
M. B. Yatvin
Keyword(s):  
Amino Acids ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Specific Radioactivity ◽  
Protein Diet ◽  
Low Protein Diet ◽  
Deficient Diet ◽  
Low Protein ◽  
Rna Content ◽  
Cytoplasmic Rna

Weanling (23-day-old) rats were fed either on an amino acid-deficient diet (6% of casein, which in effect represents an ‘amino acid-deficient’ diet) or on a diet containing an adequate amount of protein (18% of casein) for 28 days. The hepatic cells from the animals fed on the low-protein diet were characterized by low amino acid content, almost complete inhibition of cell proliferation and a marked decrease in cell volume, protein content and concentration of cytoplasmic RNA compared with cells from control rats. The lower concentration of cytoplasmic RNA was correlated with a decreased ribosomal-RNA content, of which a larger proportion was in the form of free ribosomes. The protein-synthetic competence and messenger-RNA content of isolated ribosomes from liver cells of protein-deprived animals were 40–50% of those noted in controls. At 1hr. after an injection of radioactive uridine, the specific radioactivity of liver total RNA was greater in the group fed on the low-protein diet, but the amount of label that was associated with cytoplasmic RNA or ribosomes was significantly less than that noted in control animals. From these data it was concluded that dietary amino acids regulate hepatic protein synthesis (1) by affecting the ability of polyribosomes to synthesize protein and (2) by influencing the concentration of cytoplasmic ribosomes. It is also tentatively hypothesized that the former process may be directly related to the concentration of cellular free amino acids, whereas the latter could be correlated with the ability of newly synthesized ribosomal sub-units to leave the nucleus.

AMINO ACID CONTROL OF PROTEIN SYNTHESIS AND DEGRADATION IN ISOLATED RAT HEPATOCYTES*

1980 ◽  
Vol 349 (1) ◽  
pp. 1-17 ◽  
Author(s):  
Per O. Seglen ◽  
Anne E. Solheim ◽  
Bjørn Grinde ◽  
Paul B. Gordon ◽  
Per E. Schwarze ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Amino Acid ◽  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Acid Control ◽  
Protein Synthesis And Degradation ◽  
Synthesis And Degradation ◽  
Isolated Rat
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