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PubMed1977

Partial derepression of the isoleucine-valine enzymes during methionine starvation is Salmonella typhimurium.

Methionine starvation of methionine auxotrophs in the presence of excess branched-chain amino acids results in a partial derepression of the isoleucine and valine enzymes. Reversed-phase chromatography indicated that isoleucine, valine and leucine tRNA were altered during methionine starvation. In addition, the total tRNA isolated from cells under these conditions were undermethylated. The observed derepression may be caused by the inability of methyl-deficient tRNA's to participate adequately in normal regulatory functions.

2-Isopropylmalate Synthase↗
PubMed1996

Acylcarnitine removal in a patient with acyl-CoA beta-oxidation deficiency disorder: effect of L-carnitine therapy and starvation.

Carnitine levels and acylcarnitine profiles in a patient with mild multiple acyl-CoA dehydrogenase deficient beta-oxidation were compared with control results. Whereas blood and urine total carnitine levels were moderately decreased, blood esterified carnitine levels in the patient were about 2-fold higher than in controls. Urinary acylcarnitine profiles presented with a larger variety of carnitine esters than in controls and included propionylcarnitine, butyrylcarnitine, 2-methylbutyrylcarnitine, hexanoylcarnitine and octanolycarnitine. Total carnitine levels in body fluids were similarly affected by chronic oral L-carnitine administration in patient and controls. By contrast, esterified carnitine level increase was 2-fold more important in controls than in patient. Whereas no qualitative changes in urinary acylcarnitine profiles were induced by L-carnitine therapy in controls, several alterations of these profiles were observed in the patient. The effect of starvation on metabolites was also studied, especially beta-oxidation rates assessed by free fatty acids to 3-hydroxybutyric acid ratios in blood from the patient in the untreated and L-carnitine treated states. In the L-carnitine-supplemented patient, the effect of starvation on the time course of carnitine levels and acylcarnitine profiles could also be documented. The ability of chronic oral L-carnitine administration to remove relatively less important amounts of acylcarnitines in the patient than in controls is further discussed, as well as qualitative alterations of acylcarnitine profiles induced by this therapy in the pathological condition.

Acyl-CoA Dehydrogenase↗
PubMed1984

Kinetics of G1 transit following brief starvation for serum factors.

Growing fibroblasts such as 3T3 cells are well-known to enter a quiescent state (G0) after many hours of serum deprivation. They emerge from G0 upon readdition of serum and initiate DNA synthesis about 12 h later. In this paper, we analyzed the effects of brief periods of serum deprivation on the ability of cells in G1 to initiate DNA synthesis. Exponentially growing 3T3 fibroblasts were briefly deprived of serum and their progress into S phase was monitored by autoradiography of labeled nuclei. When 10% serum was added back to cultures deprived of serum for a few hours, the progress of G1 cells into S phase was delayed for intervals far in excess of the length of the serum deprivation. Longer serum starvations resulted in longer excess delays. Several transformed 3T3 derivatives were markedly less sensitive to this serum-induced G1 regression following deprivation. When 1 microgram/ml insulin (rather than 10% serum) was added back to the starved cultures, the G1 cells entered S phase immediately. Delay in S phase entry following serum readdition was completely prevented if insulin (and, to a lesser extent, EGF) was present during the starvation, was diminished if a lower serum concentration was used for readdition, and was partially abolished if 10% serum plus insulin was restored to the cultures. The above results, then, suggest that serum deprivation sensitizes the cells to an unidentified serum component which sets the cells back in G1, unless insulin is present to maintain the flow of cells into S.

Animals↗
PubMed1992

Differential increase in activity of acid phosphatase induced by phosphate starvation in Tetrahymena.

We have studied the effects of phosphate starvation on the levels and distributions of activities of acid phosphatase and beta-hexosaminidase in cultures of Tetrahymena thermophila. The cells were grown in synthetic nutrient medium and refed every day with fresh medium. After 4 days of growth in the complete medium, the cultures were divided into two portions. One received complete medium and the other phosphate-free, but otherwise complete, medium. Population densities and activities of acid phosphatase and beta-hexosaminidase in cells plus medium and in cell-free samples were determined in aliquots removed every day before medium replacement. In cultures having complete medium the enzyme levels remained fairly constant; in the phosphate-starved cultures both total and extracellular activities of acid phosphatase increased sixfold. beta-Hexosaminidase levels remained essentially unaltered in both cases. These results indicate that phosphate starvation can induce differential increase in acid phosphatase activity in cultures of Tetrahymena. Somewhat less than 50% of the total activities of both enzymes are found in the cell-free extracellular fluid at any time.

Acid Phosphatase↗
PubMed1990

Crithidia luciliae: starvation for purines and/or phosphate leads to the enhanced surface expression of a protein responsible for 3'-nucleotidase/nuclease activity.

It has been shown previously that starvation of the trypanosomatid protozoan Crithidia luciliae for purines and/or inorganic phosphate results in increased levels of a surface membrane-associated 3'-nucleotidase/nuclease (3'-N'ase) activity which hydrolyzes both 3'-ribonucleotides and nucleic acids, thereby permitting the organisms to transport these essential nutrients across their cell membranes. A polypeptide with the requisite catalytic properties has been identified by an in situ gel activity assay following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In current studies, differential synthesis of the protein responsible for the 3'-N'ase activity was not demonstrable by comparisons of SDS-PAGE patterns of nutrient-replete or purine-starved parasites metabolically labeled with either [35S]methionine, [3H]leucine, or [3H]tyrosine. However, surface labeling of nutrient-replete and purine-starved cells revealed the enhanced expression of an 125I surface-labeled 43-kDa protein which comigrated with the 3'-N'ase activity in one- and two-dimensional electrophoretic systems. The amount of this surface-labeled peptide correlated with the level of 3'-N'ase activity as measured by test tube assay. Refeeding adenosine to purine-starved cells led to the loss of both the enzyme activity and the surface iodinatable 43-kDa band as a result of renewed cell division. Starvation of these organisms for phosphate also led to the enhanced expression of the 43-kDa radioiodinatable band. The results indicated that the 3'-N'ase protein, itself, is differentially expressed at the cell surface under conditions which lead to increased enzyme activity.

Animals↗
PubMed1992

In vivo activation of the yeast plasma membrane ATPase during nitrogen starvation. Identification of the regulatory domain that controls activation.

Yeast plasma membrane ATPase is activated during nitrogen starvation when a fermentable substrate is present. This activation is due to changes in the Vmax and it is irreversible, independent of protein synthesis and apparently triggered by a decrease in the intracellular pH. It is shown that the ATPase regulatory domain implicated in the activation by fermentable carbon sources is also implicated in activation by nitrogen starvation and by external acidification.

Adenosine Triphosphatases↗
PubMed1996

Induction of beta-methylcrotonyl-coenzyme A carboxylase in higher plant cells during carbohydrate starvation: evidence for a role of MCCase in leucine catabolism.

Induction of beta-methylcrotonyl-coenzyme A carboxylase (MCCase) activity was observed during carbohydrate starvation in sycamore cells. In mitochondria isolated from starved cells, we noticed a marked accumulation of the biotinylated subunit of MCCase, of which the apparent molecular weight of 74000 was similar to that of the polypeptide from mitochondria of potato tubers. Our results provide evidence for a role of MCCase in the catabolic pathway of leucine, a branched-chain amino acid which transiently accumulates in carbon-starved cells in relation to a massive breakdown of proteins. Furthermore, when control sycamore cells were incubated in the presence of exogenous leucine, this amino acid accumulated in the cells and no induction or accumulation of MCCase was observed, indicating that leucine is not responsible for the induction of its catabolic machinery. Finally, MCCase is proposed as a new biochemical marker of the autophagic process triggered by carbohydrate starvation.

Carbon-Carbon Ligases↗
PubMed1988

Hormonal regulation of fat body glycogen phosphorylase activity in larval Manduca sexta during starvation.

The hormonal regulation of fat body glycogen phosphorylase activity in Manduca sexta larvae was studied. During the first 3 hr of starvation the corpora cardiaca (CC) release a glycogen phosphorylase-activating hormone (GPAH). The haemolymph of 24-hr-starved larvae seems to contain increased levels of GPAH, but after 48 hr the titre can be assumed to be as low as prior to starvation. Abdominal stretch receptors do not appear to be involved in the regulation of GPAH release from the CC. Phosphorylase activation can be prevented by the injection of glucose or by feeding the animals with agar containing various carbohydrates. These treatments seem to prevent the release of GPAH from the CC rather than the action of GPAH on the fat body. The physiological signal which initiates peptide release remains unclear.

Animals↗
PubMed1984

Conformational changes in bacterial polysomes induced by amino acid starvation.

The effects of amino acid starvation on polysome conformation were analyzed comparatively in stringent (relA+) and relaxed (relA) bacteria by measuring the accessibility in vitro of ribosomal proteins to reductive methylation. In polysomes of stringent cells, the conformational state of two proteins (L13 and L29) appeared significantly changed by starvation. In polysomes isolated from relaxed mutants, the accessibility of five proteins (L5, L13, L29, L31 and L32) was found modified.

Amino Acids↗
PubMed1994

Starvation-associated mutation in Escherichia coli: a spontaneous lesion hypothesis for "directed" mutation.

When stationary phase E. coli WU3610, carrying an ochre mutation in the tyrA gene, were incubated on plates lacking tyrosine, tyrosine-independent (Tyr+) mutants appeared from day 7 onwards in a time-dependent manner. These starvation-associated mutants did not contain either identifiable tRNA suppressors or reversions at the ochre site and are thus quite distinct from the mutants commonly found to arise during active growth. When an appropriate fluctuation assay protocol was employed slow growing Tyr+ mutants were also found to arise in growing cells, and their distribution was more characteristic of a replication-dependent than a time-dependent process. The rate of appearance of starvation-associated mutants at 37 degrees C was somewhat less than at 27 degrees C and this was attributed to a reduction in viability at the higher temperature. There was no evidence for the accumulation on the plates of mutations in other genes. Tyr+ mutants were, however, shown to arise during incubation of stationary phase cells under conditions where there was no selection for tyrosine independence, provided outgrowth was subsequently permitted on plates lacking tyrosine. This distinguishes the present system from those systems exhibiting genuine "directed" or "adaptive" mutation, should they exist. To explain the specificity which occurs, it is proposed that the appearance of stationary mutants in ochre strains reflects the time-dependent accumulation in the transcribed strand of a DNA lesion that has a high probability of miscoding during transcription and replication. A mutant RNA transcript permits protein synthesis which in turn triggers DNA replication. The mutation is then fixed in the DNA as a permanent heritable change. The apparent "directedness" of the process is, on this model, determined solely by the particular miscoding DNA lesion occurring in a transcribed strand at a site where a change in phenotype permits DNA replication to occur.

Culture Media↗
PubMed1995

Starvation-associated mutation in Escherichia coli strains defective in transcription repair coupling factor.

When E. coli WU3610 (tyrA14 ochre) bacteria are starved of tyrosine on the surface of glucose-salts agar plates, there is a progressive accumulation of slow growing prototrophic mutants that are neither revertants at the ochre codon nor any of the well characterised tRNA ochre suppressors. Isogenic derivatives defective in transcription repair coupling factor (mfd) showed normal starvation-associated mutation (SAM). WU361045, the original mfd strain, showed very much reduced SAM. At 37 degrees C this was associated with progressive loss of viability on plates but the defect in SAM was not due to loss of viability since incubation at 27 degrees C or addition of catalase prevented the loss of viability but did not restore SAM. Furthermore, mutants could not be rescued from starved WU361045 populations by a short period of tyrosine supplementation arguing that WU361045 was defective not in the survival of starvation-associated mutants, but in their formation. The SAM defect in WU361045 was not complemented by the katF gene on a low copy number plasmid. It is concluded that WU361045 carries an unidentified mutation, not under katF control, that greatly reduces SAM. If SAM is attributable to a spontaneously occurring DNA lesion, the latter is unlikely to be formed by hydrogen peroxide or active species derived from it.

Adaptation, Biological↗
PubMed1987

The yeast polyubiquitin gene is essential for resistance to high temperatures, starvation, and other stresses.

Conjugation of ubiquitin to intracellular proteins mediates their selective degradation in eukaryotes. In the yeast Saccharomyces cerevisiae, four distinct ubiquitin-coding loci have been described. UBI1, UBI2, and UBI3 each encode hybrid proteins in which ubiquitin is fused to unrelated sequences. The fourth gene, UBI4, contains five ubiquitin-coding elements in a head-to-tail arrangement, and thus encodes a polyubiquitin precursor protein. A precise, oligonucleotide-directed deletion of UBI4 was constructed in vitro and substituted in the yeast genome in place of the wild-type allele. ubi4 deletion mutants are viable as vegetative cells, grow at wild-type rates, and contain wild-type levels of free ubiquitin under exponential growth conditions. However, although ubi4/UBI4 diploids can form four initially viable spores, the two ubi4 spores within the ascus lose viability extremely rapidly, apparently a novel phenotype in yeast. Furthermore, ubi4/ubi4 diploids are sporulation-defective. ubi4 mutants are also hypersensitive to high temperatures, starvation, and amino acid analogs. These three conditions, while diverse in nature, are all known to induce stress proteins. Expression of the UBI4 gene is similarly induced by either heat stress or starvation. These results indicate that UBI4 is specifically required for the resistance of cells to stress, and that ubiquitin is an essential component of the stress response system.

Alleles↗
PubMed1994

Starvation in vivo for aminoacyl-tRNA increases the spatial separation between the two ribosomal subunits.

Structures in situ of individual ribosomes in E. coli have been determined by computer-aided electron microscope tomography using a tilt series of positively stained embedded cellular sections. Amino acid starvation of a bacterial culture, causing a deficiency for aminoacyl-tRNA, induces a spatial separation between the ribosomal subunits compared with ribosomes in exponentially growing cells. Eight ribosomes from each growth condition were aligned to each other, and the two average structures were determined. Comparison of these suggests that the distance between the two subunits increases by approximately 3 nm upon starvation for aminoacyl-tRNA during protein synthesis. Ribosomes in most other states of the translational elongation cycle in exponentially growing cells show a more compact structure than previously realized.

Amino Acids↗
PubMed1996

Protection of B lymphocyte hybridoma against starvation-induced apoptosis: survival-signal role of some amino acids.

The phenomenon of starvation-induced apoptosis was studied in cultures of a mouse B lymphocyte hybridoma. In a continuous culture the limitation of nutrients was modelled by dilution of a protein-free medium with saline to 15%. Surprisingly, the hybridoma clone did not die out under extreme starvation conditions. A steady state was established in which the cells continued to grow at very low viable cell concentration, concomitantly with an enhanced rate of apoptotic death. Suppression of the death rate, and increase of steady-state viable cell concentration, could be achieved by additions of L-alanine, L-asparagine or L-glutamine, but not by addition of L-phenylalanine. This specificity pattern is in agreement with previous screening experiments that have identified a set of apoptosis-preventing amino acids (glycine, L-alanine, L-serine, L-threonine, L-proline, L-asparagine, L-glutamine, L-histidine). The analysis of amino acid consumption and production showed a consistent production of alanine and serine both in standard medium and in diluted media. When alanine was added at a final concentration of 2 mM to media diluted either to 40 or 20%, apoptosis was partly suppressed. A limited production of alanine was observed also in alanine-enriched diluted media. It is concluded that the apoptosis-preventing amino acids act as signal molecules, besides their nutritive function, and that the signal has a character of a survival factor. The observed phenomena are interpreted in terms of a survival-control mechanism that regulates the viable cell number of a lymphocyte clone in an adequate proportion with the level of available nutrients.

Amino Acids↗
PubMed1988

Protein synthesis in polyamine-deficient bacteria during amino-acid starvation.

Amino-acid starvation in polyamine-auxotrophic bacteria grown in the presence of putrescine provokes a marked inhibition of protein synthesis. This inhibition is almost completely relieved in polyamine-depleted cells. The differential behaviour of bacterial protein synthesis depending on the endogenous levels of polyamines is not due to a change in the uptake of amino acids used to measure protein synthesis, nor to the decreased growth rate of polyamine-depleted cells. During leucine starvation, cells grown with putrescine synthesized a somewhat lower amount of high-molecular-weight proteins than polyamine-depleted bacteria. In addition, cells with normal endogenous levels of polyamines accumulated significant amounts of 62 and 41 kDa polypeptides as well as several low-molecular-weight peptides.

Amino Acids↗
PubMed1990

Effect of starvation on work capacity and voluntary skeletal muscle function in man.

Post-operative fatigue is a well-known clinical problem even after uncomplicated surgery. In the multifaceted post-operative state, several factors other then the surgical trauma may influence muscular function, such as an insufficient nutritional intake. The aim of this study was to investigate the effect of fasting on work capacity and voluntary skeletal muscle function. Eight healthy lean volunteers, age range 25-43 years, were studied the day before starvation, at the end of the fasting period of 5 days, and after another 3-4 days on a normal diet. Hand grip strength was assessed as maximum voluntary contraction (MVC) and physical working capacity was investigated with successively increased work load on a cycle ergometer until near exhaustion. After 5 days of total starvation, MVC remained unchanged but physical working capacity was reduced from 220 +/- 18 watt to 199 +/- 22 watt (p < 0.05). Corresponding heart rate, estimated effort and leg tiredness were not changed. A poor nutritional intake per se may therefore be a less important factor causing post-operative muscle fatigue than the operation itself.

Journal Article↗
PubMed1990

Effects of hysterectomy and semi-starvation on amino-acid gradients across liver, muscle and gut in rats.

To study the effects of surgical stress and insufficient food intake on amino-acid exchange of liver, gut, and muscle, blood was sampled in random sequence from the aorta, the inferior caval vein, the portal vein, and the hepatic veins in 3 groups of 20 rats each. Control rats were fed ad libitum, hysterectomised rats were studied on the first and third post-operative day, and semi-starved rats were pair-fed to hysterectomised rats to an intake of 13% of control on the first day. Both groups lost 5-8% of body weight. Surgery increased the concentration gradient (release) of urea across liver by 60%, the glucose gradient (release) by 35%, and doubled the concentration gradients (uptake) across liver of alanine, arginine, glycine, lysine, proline, serine, and threonine, and decreased their plasma concentrations. There was no major change in hepatic amino-acid gradients in semi-starved animals, and there was no appreciable change in gradients of single amino-acids across gut or muscle in animals subjected to surgery or semi-starvation. Post-surgical increases in urea synthesis and hepatic uptake of uragenic and gluconeogenic amino-acids are due to the surgical stress and not to the post-operative semi-starvation.

Journal Article↗
PubMed1991

Polychlorinated biphenyls in oystercatchers (Haematopus ostralegus) from the oosterschelde (Dutch Delta area) and the Western Wadden Sea, that died from starvation during severe winter weather.

Wintering oystercatchers (Haematopus ostralegus), charadriid shorebirds that chiefly feed on intertidal bivalves, suffered mass mortality in The Netherlands during severe frosts in 1986 and 1987. PCBs were analysed in liver and (partially) brain lipids of 96 birds to examine the influence of age (three categories), sex and wintering area (the Oosterschelde estuary versus the westernmost Wadden Sea) on levels, and the risk of intoxication due to starvation. Victims had lost nearly 40% of their normal winter weight. PCB-structures were similar in all age/sex categories, and in both areas. Sex did not affect total PCB-concentrations. First-winter Wadden birds had lower levels than subadults and adults, but an age-difference was absent in the Oosterschelde birds. Some juvenile outliers possibly originated from polluted breeding areas. Individual variation was considerable in most categories. Relevant ecological factors are discussed. Although a dam has considerably reduced the direct transport of PCBs into the Oosterschelde since 1969, contamination of local birds was hardly lower than in Wadden winterers. Influx of riverine PCBs into the Oosterschelde from coastal water may have been underrated. Starvation increased liver concentrations by a factor of 35; factors for the brain were 56 for juveniles and approximately 120 for older birds. Considering published lethal levels for other species, it is doubtful if PCBs contributed to this winter mortality.

Journal Article↗