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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Amino acids adsorbed onto blood cell membranes represent about 8% of the total amino acids in blood. The aim of this study was to determine the in vitro adsorption kinetics of different amino acids (L-alanine, glycine, L-glutamate, L-glutamine, L-phenylalanine and L-leucine) onto rat erythrocyte membranes and to assess the effect of 24-hr starvation on these adsorption kinetics. Isolated red cell membranes were incubated at 37 degrees C for 10 sec in the presence of 14C-amino acids--with different specific radioactivity--the radioactivity retained in the membrane fraction measured and kinetic parameters of amino acid adsorption determined. With the exception of glutamate, where the adsorption was negligible, all amino acids studied were adsorbed onto isolated red cell membranes, adhering to simple Michaelis-Menten kinetics. Km' values of glycine, phenylalanine and leucine adsorption in control rats (14.7 +/- 3.8 mM, 8.41 +/- 0.95 mM and 4.65 +/- 0.46 mM respectively, SEM, n = 6-8) decreased in response to 24-hr starvation, giving the following values: 0.792 +/- 0.122 mM, 5.32 +/- 0.82 mM and 3.53 +/- 0.31 mM respectively (SEM, n = 6-8), Vmax' value of glycine adsorption of control rats decreased (from 61.0 +/- 15.5 mmol/mol P/sec to 4.25 +/- 0.70 mmol/mol P/sec, SEM, n = 7) and that of leucine increased (from 13.5 +/- 1.0 mmol/mol P/sec to 18.9 +/- 2.0 mmol/mol P/sec, SEM, n = 7) as an effect of 24-hr starvation. This study shows that alanine, glycine, glutamine, phenylalanine and leucine, but not glutamate, adsorbed onto erythrocyte membranes according to Michaelis-Menten-like kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:In vitro adsorption of amino acids onto isolated rat erythrocyte membranes. 758 9

The kinetic parameters of the L-phenylalanine and L-leucine uptake by isolated erythrocytes in fed and 24 hour starved rats have been determined. In addition, the in vivo compartmentation between blood cells and plasma of the above amino acids in arterial and venous blood vessels has also been studied under the above physiological situations. Both the L-phenylalanine and L-leucine uptake by erythrocytes was saturable and non concentrative. Starvation increased the Km value for the leucine uptake and did not significantly affect that of phenylalanine uptake. The in vivo blood cell/plasma (C/P) concentration ratio of both amino acids was higher than the unit. The starvation-induced changes in the relative distribution of these amino acids between the blood cell and the plasma compartments were significant for the phenylalanine in the aortic artery but not in venous blood. The transport system capabilities measured in vitro can not account for the maintenance of both the leucine and phenylalanine gradient between blood cells and plasma, and the starvation-induced changes in the blood amino acids compartmentation are not directly related entirely to the transport system capabilities.
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PMID:Erythrocyte uptake kinetics and cell to plasma gradients of leucine and phenylalanine in fed and fasted rats. 768 63

Strain 129 is a fragmentation mutant of the filamentous cyanobacterium Anabaena sp. strain PCC 7120. Growing with fixed nitrogen, this mutant forms filaments that are much shorter than wild-type filaments. Following starvation for fixed nitrogen, strain 129 becomes nearly unicellular and forms few heterocysts, although electron microscopy suggests that proheterocysts form while fragmentation occurs. Starvation for sulfate, phosphate, iron, and calcium does not cause this fragmentation. The affected gene in strain 129, fraC, was cloned by complementation and characterized. It encodes a unique 179-amino-acid protein rich in phenylalanine. Insertional inactivation of the chromosomal copy of fraC results in a phenotype identical to that of strain 129, while complementation using a truncated version of FraC results in only partial complementation of the original mutant. Heterocysts could be induced to form in N-replete cultures of strain 129, as in wild-type cells, by supplying extra copies of the hetR gene on a plasmid. Thus, FraC is required for the integrity of cell junctions in general but is apparently not directly involved in normal differentiation and nitrogen fixation.
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PMID:A short-filament mutant of Anabaena sp. strain PCC 7120 that fragments in nitrogen-deficient medium. 788 9

Preparative isoelectric focusing and gel filtration chromatography were used to purify a carboxypeptidase produced by the entomopathogenic fungus Metarhizium anisopliae during growth on cockroach cuticle. The enzyme was inhibited by diisopropyl fluorophosphate, implying involvement of a serine residue in catalysis. However, the M. anisopliae enzyme differed from most serine carboxypeptidases in also being inhibited by the metal chelator 1,10-phenanthroline and in being a small (30 kDa), basic (pI 9.97) protein with a neutral pH optima (pH 6.8). These properties resemble those exhibited by some metalloproteases but the enzyme is not inhibited by Cd2+; nor do Zn2+ or Co2+ restore activity in enzyme inhibited with phenanthroline. The amino-terminal sequence (22 residues) showed no similarity to other protein sequences. Unlike previously reported fungal carboxypeptidases, the M. anisopliae enzyme is powerfully inhibited by potato carboxypeptidase inhibitor. The carboxypeptidase shows a broad primary specificity toward amino acids with hydrophobic side groups in a series of N-blocked dipeptides, with substrates with phenylalanine being the most rapidly hydrolyzed. The S1 subsite also accommodated Glu, confirming its low selectivity. Proline at P1 or P1 resulted in a very poor substrate. The specificity of the carboxypeptidase complements that of the subtilisin-like protease (Pr1) of M. anisopliae. Both Pr1 and the carboxypeptidase are produced during carbon and nitrogen deprivation, which indicates that the exopeptidase functions with Pr1 to degrade peptides to supply amino acids during starvation and pathogenicity.
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PMID:Characterization of a novel carboxypeptidase produced by the entomopathogenic fungus Metarhizium anisopliae. 797 80

Amino acid deprivation of the bovine renal epithelial cell line NBL-1 led to a range of responses by the heat shock and glucose regulated stress proteins. The classic heat shock induction of HSP 72 was found to be mimicked, without prior heat stress, by phenylalanine addition to cells simultaneously deprived of all other amino acids. Co-inclusion of alanine prevented the HSP 72 induction by phenylalanine but not that caused by heat stress. Phenylalanine also increased expression of HSP 70 mRNA in cells simultaneously deprived of other amino acids. The glucose regulated protein GRP 75 was increased upon amino acid deprivation. GRP94 was detectable in a 50 kDa form in control cells but was detected as a 94 kDa form upon amino acid deprivation which was further enhanced upon inclusion of phenylalanine. Addition of alanine to the starvation medium led to detection of the 50 kDa form only. Amino acid deprivation appears to mimic the glucose deprivation stress response. Inclusion of phenylalanine during amino acid deprivation leads to a stress response similar to that of heat shock in terms of HSP 72 induction. However, the two inducers are sensitive to different repression signals since only the phenylalanine-signal was subject to nihilation by alanine co-inclusion.
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PMID:Amino acid deprivation-induced stress response in the bovine renal epithelial cell line NBL-1: induction of HSP 70 by phenylalanine. 798 Dec 32

Schizosaccharomyces pombe h+ cells secrete a diffusable mating pheromone called P-factor. Here we show that the map2 gene, a defect of which confers h(+)-specific sterility, encodes the precursor of P-factor. We purified P-factor from cells overexpressing map2 and determined its amino acid sequence. P-factor is a peptide of 23 residues, with the sequence Thr-Tyr-Ala-Asp-Phe-Leu-Arg-Ala-Tyr-Gln-Ser- Trp-Asn-Thr-Phe-Val-Asn-Pro-Asp-Arg-Pro-Asn-Leu. A synthetic peptide of this sequence gave the same specific activity and chromatographic profile as the purified P-factor, suggesting that P-factor is unmodified. h- cells starved for nutrition showed a morphological response to P-factor. Transcription of the sxa2 gene, which encodes a protease thought to degrade P-factor, was activated in these cells. The cry1 null mutant, which lacks adenylyl cyclase and has little intracellular cAMP, was susceptible to P-factor even in the presence of nutrients. Combination of the cyr1 and sxa2 mutations enhanced this susceptibility. P-factor induced not only responses toward mating but also arrest of the cell cycle at the G1 phase in h- cyr1 sxa2 cells. This proves that the S. pombe mating pheromone has the ability to arrest cell cycle progression, which has previously been obscured by the usual requirement for mating of nutritional starvation and subsequent growth arrest.
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PMID:The fission yeast mating pheromone P-factor: its molecular structure, gene structure, and ability to induce gene expression and G1 arrest in the mating partner. 831 86

Simultaneous lipogenesis and protein synthesis as influenced by LY79771, testosterone, or dehydroepiandrosterone in starved/refed rats were studied. Starved-refed BHE/cdb rats were injected with one of these compounds during the 2-day refeed period. Hepatic de novo fatty acid synthesis using tritium incorporation into fatty acids and protein synthesis using [14C]phenylalanine incorporation into hepatic and muscle protein were determined. Hepatic lipogenesis was decreased by all three drugs and these drugs had a differential effect on protein synthesis. We did not observe a corresponding increase in protein synthesis in the liver when fat synthesis was decreased, but we did observe a corresponding increase in muscle protein synthesis. We concluded that in the acute hyperlipogenic state induced by starvation/refeeding, these drugs induced a reciprocal increase in muscle protein synthesis along with a suppression of fatty acid synthesis.
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PMID:Drugs that suppress hepatic fat synthesis in starved-refed BHE/cdb rats also have an effect on muscle protein synthesis. 841 72

1. Protein loss in muscle can be caused by decreased protein synthesis, increased breakdown or both. In small animals the tracer incorporation technique is mostly used to measure protein synthesis, but for degradation measurements in vitro or ex vivo settings are required. In human and large animal studies the arteriovenous dilution technique is used because it enables the measurement of synthesis and breakdown rates simultaneously. The applicability in small animals has not yet been proven. We used a starvation model to compare both techniques. 2. A primed constant infusion of L-[2,6-(3H)]phenylalanine was given to male Lewis rats after 16, 40, 64 and 112 h starvation. Protein synthesis rates of the gastrocnemius muscle were measured by the incorporation technique and compared with hindquarter protein turnover calculated in a two- and three-compartment arteriovenous dilution model. 3. Whole-body phenylalanine rate of appearance decreased from 456 +/- 32 after 16 h to 334 +/- 34 (nmol min-1 100 g-1 body weight) after 112 h starvation. Protein synthesis rates of the gastrocnemius muscle measured by the tracer incorporation technique decreased from 3.6 +/- 0.4 after 16 h starvation to 2.2 +/- 0.3 after 64 h starvation and 1.8 +/- 0.4 (%/day) after 112 h starvation. Hindquarter protein breakdown, calculated with the tracer dilution model, increased after 112 h starvation from 28 +/- 12 to 77 +/- 15 nmol min-1 100 g-1 body weight. Using the tracer dilution model, however, the calculated protein synthesis rate across the hindquarter also increased after prolonged starvation (29 +/- 7 and 68 +/- 16 nmol min-1 100 g-1 body weight after 16 and 112 h respectively). In conjunction with this, calculated bidirectional membrane transport rates were also enhanced. Using valine and glutamine as tracers, the enhanced amino acid turnover rates were confirmed. 4. In conclusion, our results show that during short periods of starvation both methods give similar results. After prolonged starvation, however, an opposite change in disappearance rate and protein synthesis rate was observed. Assumptions made to calculate protein turnover using the arteriovenous dilution model may account for the discrepancy and care must be taken with the interpretation when using only one model in anaesthetized small animals.
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PMID:Muscle protein and amino acid turnover in rats in vivo: effects of short-term and prolonged starvation. 869 15

During starvation, splanchnic organs are proportionally more affected by protein loss than other organs. Amino acid membrane transport is one of the regulating mechanisms of protein turnover, but until now in vivo data were lacking. To study in vivo phenylalanine and tyrosine membrane transport and protein turnover in splanchnic organs, a primed continuous infusion of L-[2,6-3H]phenylalanine was given to control rats (postabsorptive) and after short (40 h) and prolonged (112 h) starvation. Data were analyzed using a three-compartment model previously used in muscle membrane transport studies. Inward and outward amino acid plasma-tissue membrane transport rates in both the liver and gut were upregulated after prolonged starvation. Metabolic shunting of phenylalanine and tyrosine increased in the gut but decreased to zero in the liver after prolonged starvation. In conjunction with this, gut and liver protein turnover increased after prolonged starvation. In the liver the net uptake of gluconeogenic precursors also increased, indicative for increased gluconeogenesis. The observed changes in amino acid metabolism in both splanchnic organs after prolonged starvation may reflect an adaptation of the gut and liver to nutritional deprivation and could be of benefit during refeeding.
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PMID:In vivo amino acid metabolism of gut and liver during short and prolonged starvation. 877 72

Measurement of amino acid kinetics using muscle exchange rates of labeled phenylalanine and leucine has been successfully used to estimate in vivo protein synthesis and degradation rates in human forearm and in hindlimb of large laboratory animals. No good method to measure protein breakdown in muscle of small laboratory animals is available, and we therefore investigated whether this technique can be applied to rats. Using [3H]phenylalanine-exchange measurements, protein synthesis and degradation rates were measured in muscle of fed and 2-day starved rats. Protein synthesis rates obtained in this way were compared with rates measured with the phenylalanine flooding-dose technique in sham-cannulated (including anesthesia and surgery) fed and fasted rats and in awake fed rats. Using the [3H]phenylalanine-exchange method, protein synthesis rates in 2-day starved rats were increased to 292% and protein degradation rates to 217% of the values obtained in fed rats. However, due to a high variation, these changes were not statistically significant. Results obtained with the flooding-dose technique indicate that 2-day starvation reduced protein synthesis rates to 61% of the fed value. However, protein synthesis rates measured with the flooding-dose technique were decreased by 40% in sham-cannulated fed rats in comparison to awake fed rats. An additional 19% reduction in adenosine triphosphate (ATP) concentration in the muscle of the same rats shows that the procedure necessary to apply the exchange measurements to rats has a significant influence on the physiology of the muscle. We therefore conclude that [3H]phenylalanine-exchange measurements as applied in this study are of limited value to estimate in vivo protein synthesis and degradation rates of individual tissues in rats.
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PMID:Tracer kinetics are of limited value to measure in vivo protein synthesis and degradation rates in muscle of anesthesized rats. 884 85


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