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

Development of multicellular fruiting bodies of Myxococcus xanthus can be induced by limitation of any of a number of different classes of amino acids. Investigated were amino acids that wild-type strains of M. xanthus are unable to synthesize (isoleucine, leucine, and valine), can synthesize at a low rate (phenylalanine), or can normally synthesize at an adequate rate (tryptophan and serine). In general, gradual rather than abrupt starvation for an essential amino acid was required for the induction of fruiting. Perhaps gradual starvation in general minimizes antagonism between amino acids present in the medium, as was documented for valine starvation. The previously reported induction of fruiting by a high concentration of threonine was shown to be specifically reversed by lysine. Threonine addition may starve cells for lysine by feedback inhibition of aspartokinase activity. Starvation for carbon-energy sources or inorganic phosphate also induced fruiting. As in other bacteria, amino acid starvation of M. xanthus leads to increases in cellular guanosine polyphosphate, usually consisting of large increases in the amount of guanosine pentaphosphate with smaller increases in the level of guanosine tetraphosphate. Guanosine polyphosphate accumulation is thus shown to be correlated with nutritional conditions that induce fruiting, and therefore may serve as an intracellular signal to trigger cells to end vegetative growth and initiate fruiting body development.
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PMID:Guanosine pentaphosphate and guanosine tetraphosphate accumulation and induction of Myxococcus xanthus fruiting body development. 676 42

Evidence was found which indicated that a mutation in gene trpS affected the rate of synthesis of tyrosine-repressible 3-deoxy-D-arabinoheptulosonic acid-7-phosphate (DAHP) synthetase. The effect was found to occur independently of repression mediated by the tyrR gene product, and it was not due to a change in growth rate, nor was it a manifestation of the stringent response. It is proposed that in the proximal region of the aroF-tyrA operon there is an attenuator site controlled by the level of charged tryptophanyl-transfer RNA. In addition, it was demonstrated that starvation for certain amino acids led to degradation of tyrosine-repressible DAHP synthetase, but not phenylalanine-repressible DAHP synthetase, and supplementation with the missing amino acid led to an increased rate of synthesis of tyrosine-repressible DAHP synthetase during subsequent growth.
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PMID:Regulation of aromatic amino acid biosynthesis in Escherichia coli K-12: control of the aroF-tyrA operon in the absence of repression control. 678 75

1. Rates of appearance and oxidation of plasma L-leucine, L-phenylalanine and L-tyrosine, as well as conversion of plasma phenylalanine into plasma tyrosine, were determined in 90-120 g rats after overnight starvation and while receiving 115-120 mumol of L-phenylalanine/h. 2. In the post-absorptive state, plasma tyrosine and phenylalanine appearances were similar, despite the fact that 22% of plasma tyrosine appearance could be attributed to the hydroxylation of phenylalanine. 3. A constant infusion of 115-120 mumol of L-phenylalanine/h did not significantly alter plasma leucine kinetics, but increased appearance of plasma phenylalanine and tyrosine. The percentage of phenylalanine and tyrosine appearance that was oxidized increased from 12.1% and 24.4% to 37.3% and 48.0% respectively. In phenylalanine-loaded rats, 72% of plasma tyrosine appearance could be attributed to the conversion of phenylalanine. 4. Whole-body tyrosine oxidation measured from a continuous infusion of either L-[14C]tyrosine or L-[14C]phenylalanine differed by 165%. 5. It can be concluded that, in the post-absorptive state, phenylalanine hydroxylation makes a substantial contribution to the plasma appearance of tyrosine and is significantly increased when phenylalanine is administered. The disposal of excess infused phenylalanine is a result of a greater percentage of plasma phenylalanine being converted into tyrosine and a greater proportion of tyrosine being further oxidized. However, apparent tyrosine oxidation rates estimated from plasma tyrosine specific radioactivities and appearance of expired 14CO2 during administration of [14C]tyrosine are underestimates of true rates, in part because tyrosine generated from phenylalanine hydroxylation is catabolized without freely equilibrating with the plasma compartment.
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PMID:The contribution of phenylalanine to tyrosine metabolism in vivo. Studies in the post-absorptive and phenylalanine-loaded rat. 687 Aug 7

The degradation of three types of anomalous proteins, e. g. those containing the arginine analog kanavanine; polypeptides synthesized in the presence of puromycin (100 micrograms/ml) under slight inhibition of total translation, and polypeptides synthesized under amino acid deficiency, was studied. In order to measure the rate of proteolysis, the E. coli cells were labelled for 5 min with [14C]-phenylalanine and then transferred to a complete medium. The loss of TCA-insoluble material was taken as a measure of proteolysis. While the normal total protein of E. coli cells was degraded at the rate of 2--8% per hour, the canavanine-containing proteins were degraded at the rate of 30--40% per hour. The polypeptides synthesized in the presence of puromycin were degraded at the rate of 10--15% per hour, while the polypeptides formed under amino acid starvation--at the rate of 7--8% per hour. The rate of proteolysis of canavanine-containing polypeptides was two times lower under inhibition of translation by chloramphenicol, tetracycline of kasugamicin, while the rate of degradation of two other types of anomalous polypeptides was significantly increased. Tetracycline at concentrations significantly exceeding those sufficient for maximal inhibition of translation, practically completely repressed the proteolysis of canavanine-containing proteins. No such tetracycline activity was observed in the presence of 20 mM Mg2+, which was assumed to be dependent on the complexon-forming ability of the antibiotic.
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PMID:[Role of protein synthesis in the process of degradation of anomalous proteins in Escherichia coli cells]. 701 90

The quantitative significance of the conversion in vivo of L-[U-14C]leucine to ketone bodies was determined in rats starved for 3 or 48 h. In animals starved for 3 h, 4.4% of ketone-body carbon is derived from the metabolism of leucine, and in rats starved for 48 h the corresponding value is 2.3%. This conversion occurs rapidly, and the specific radioactivity of ketone bodies in blood is maximal at 2 min after the intravenous injection of labelled leucine for both periods of starvation. The flux of leucine in the blood is 1.01 and 1.04 mumol/min per 100 g body wt. respectively for animals starved for 3 and 48 h. The specific radioactivity of blood ketone bodies was compared at 2 min after the injection of labelled leucine, lysine and phenylalanine. The specific radioactivity was 4-5 fold higher with leucine than with lysine or phenylalanine.
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PMID:The role of leucine in ketogenesis in starved rats. 711 36

Experiments with administration of phenylalanine were made to study its content in the blood and urine of young and old intact rabbits, as well as under the starvation-simulated restriction of protein synthesis. The old animals manifested an increased rate of phenylalanine increment, and of its excretion with the urine, apart from the reduced tyrosine biosynthesis. Starvation counteracts the age-associated differences as regards the body response to phenylalanine administration, with a tendency towards more distinctive shifts being seen in the young animals. It is concluded that with age the rate of assimilation and hydroxylation of phenylalanine diminishes and the possibilities of its use to meet tyrosine requirements get restricted. It is recommended that amino acids and protein supply be restricted during aging.
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PMID:[Effect of experimental starvation on the age-related characteristics of phenylalanine metabolism]. 712 97

Regulation of A system amino acid transport was studied in primary cultures of the R3230AC mammary adenocarcinoma. Higher rates of carrier-mediated Na+-dependent proline transport, vc, was decreased and was attributed to a two-fold decrease in Vmax and a two-fold increase in Km. When compared to cells grown in standard media (Eagle's minimal essential medium, MEM), cells grown in media supplemented with A system substrates (alanine, serine, glycine, and proline) demonstrated adaptive decreases in proline transport; the decrease was due to two-fold reduction in Vmax, with no change in Km for proline. Even in the presence of preferred substrates for the A system, a density-dependent decrease in proline transport was manifested. Both fast- and slow-growing cultures maintained in MEM exhibited rapid increases in proline transport when switched to buffers devoid of amino acids; two-fold increases in Vmax were seen within 4 hr, but Km was unchanged. This starvation-induced adaptation was completely prevented by inclusion in the buffer of 10 mM proline, 0.1 mM alpha-(methylamino)-isobutyric acid (MetAIB) or 10 mM serine, whereas inclusion of the poorer A system substrate, phenylalanine (10 mM), had no effect. The effects of MetAIB to prevent starvation-induced increases in proline transport were dose-related, rapid, and reversible. Amino acid starvation-induced increases in proline transport were partially blocked by cycloheximide or actinomycin D. Data were obtained demonstrating a temporal relationship between increasing intracellular [proline] and decreasing vc for proline uptake. In addition, efflux of proline from preloaded cells preceded the increase in initial rates of proline entry. Taken together, we concluded that: 1) A system transport in primary cultures of this mammary adenocarcinoma is regulated by cell density as well as by availability of A system substrates, but these two types of regulation are kinetically distinct; and 2) starvation-induced enhancement of proline transport appears to be due to release from transinhibition, but may also involve a derepression-repression type of mechanism.
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PMID:Influence of proliferative rates and A system substrate availability on proline transport in primary cell cultures of the R3230AC mammary tumor. 746 29

Using fusions between the Escherichia coli genes argI and lacZ, it has been demonstrated that ribosomal frameshifting occurs at a frequency of between 3% and 16% within the argI mRNA, soon after the initiation codon. The frameshift involves a phenylalanyl-tRNA shifting into the +1 frame at the sequence UUU-U/C. The shift does not occur if the in-frame phenylalanine codon UUU is replaced by UUC. The level of frameshifting is higher in dense cultures and is not dependent on phenylalanine starvation. In the wild-type argI gene this frameshifting event would be an error, leading to a truncated, non-functional protein. Therefore, it is unlike the numerous examples of required frameshifting events that have been described in other genes.
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PMID:A ribosomal frameshifting error during translation of the argI mRNA of Escherichia coli. 751 62

alpha-(Methylamino)isobutyric acid (MeAIB) insensitive Na(+)-dependent alanine transport activity in the bovine kidney cell line NBL-1 was increased upon amino acid starvation (> or = 20% over control levels). When L-phenylalanine (3 mM) was included in the starvation medium the increase was further enhanced (> or = 85% over control levels). In cells grown in control medium the Vmax, for MeAIB-insensitive Na+/alanine co-transport was found to be 6.0 +/- 0.7 nmol/3 min per mg (Km 41 +/- 12 microM) and for L-phenylalanine-treated amino-acid-starved cells the Vmax. was 21 +/- 5 nmol/3 min per mg (Km 92 +/- 40 microM). The increase in Vmax. was prevented by cycloheximide. Substrate specificity analysis identified the L-phenylalanine-induced transport system as System B0. [35S]Methionine labelling of cells during the amino acid starvation/phenylalanine treatments resulted in the differential labelling of a protein of 78 kDa. Northern-blot analysis using a SAAT1-specific probe revealed the presence of a new transcript (3.2 kb) in RNA extracted from cells incubated in amino acid starvation medium with L-phenylalanine included. The present findings suggest a novel means of control for System B0 by the use of physiological stress. It is also proposed that SAAT1 and System-B0 transcripts have considerable sequence similarity.
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PMID:Regulation of System B0 amino-acid-transport activity in the renal epithelial cell line NBL-1 and concomitant changes in SAAT1 hybridizing transcripts. 751 9

To examine the effect of malnutrition on liver protein metabolism and synthesis during liver regeneration, 104 rats were allocated to semi-starvation or ordinary food intake for 1 week. Half of each group was sham operated and the other half was partially hepatectomized. Specimens were taken from the liver at the time of liver resection and from animals killed 24, 48 and 72 h after the primary operation. Liver samples were analysed for DNA and protein, and in the 48-h groups RNA and protein synthesis were also analysed. Protein synthesis was measured by the flooding method using L[4-3H] phenylalanine. The liver weight during regeneration increased very rapidly in the well-nourished animals, but when expressed as percent of body weight or as proportional increases, the difference between well-nourished and malnourished animals disappeared. The fractional rate of protein synthesis was not changed in sham-operated malnourished or well-nourished animals. During regeneration, protein synthesis in well-nourished animals was elevated compared to sham-operated controls, but a lesser stimulation was seen in malnourished rats. It was concluded that the mechanism of liver regeneration depends on nutritional state, involving an increase in protein synthesis in well-nourished animals, but relying more on a decrease in protein degradation or cessation of secretory protein synthesis in malnourished animals.
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PMID:Protein synthesis in regenerating rat liver during malnutrition. 752 36


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