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

In animal tissues the pyruvate dehydrogenase complex is regulated by product inhibition and by a phosphorylation-dephosphorylation cycle catalysed by a kinase and a phosphatase. Physiologic and molecular aspects of this regulation are reviewed, and the results of recent studies are described. Insulin deficiency in the rat (diabetes or starvation) is shown to inhibit the conversion of inactive (phospho-) complex into active (dephospho-) complex by the phosphatase by an effect on the substrate for the phosphatase (phosphorylated complex). This change is stable and persists during isolation, incubation, and extraction of mitochondria or purification of phosphorylated complex. The subunit ratios in the purified pig heart pyruvate dehydrogenase complex and the stoichiometry of phosphorylations have been determined by radioamidination and incorporation of 32P. The ratios of decarboxylase tetramer (alpha 2, beta 2) : dihydrolipoyl acetyltransferase monomer : dihydrolipoly dehydrogenase monomer were 1:1:0.5. Inactivation of the complex was accomplished by incorporation of a single phosphate into one alpha subunit of the decarboxylase tetramer. Two further phosphates are then incorporated and these additional phosphorylations inhibit reactivation of the complex by the phosphate. It is suggested that multisite phosphorylations may inhibit reactivation of the complex by the phosphatase in diabetes and in starvation.
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PMID:Regulation of pyruvate dehydrogenase by insulin action. 23 84

In addition to the constitutive, low-affinity phosphate-transport system described previously, Neurospora possesses a second, high-affinity system which is derepressed during phosphorus starvation. At pH 5.8, System ii has a K1/2 of about 3muM and a Jmax of 5.2 mmol/1 cell water per min. System ii reaches maximal activity after about 2 h of growth in phosphorus-free minimal medium. Its formation is blocked by cycloheximide and, once made, it appears to turn over rapidly. Addition of cycloheximide to fully derepressed cultures results in the decay of System ii with a t1/2 of 14 min, very similar to the turnoacteriol. 95, 959-966) for tryptophan transport in Neurospora. Thus, these transport systems appear to be regulated by a balance between synthesis and breakdown, as affected by intracellular pools of substrate or related compounds.
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PMID:Phosphate transport in Neurospora. Derepression of a high-affinity transport system during phosphorus starvation. 23 36

The rate of transport of L-amino acids by Saccharomyces cerevisiae epsilon 1278b increased with time in response to nitrogen starvation. This increase could be prevented by the addition of ammonium sulfate or cycloheximide. A slow time-dependent loss of transport activity was observed when ammonium sulfate (or ammonium sulfate plus cycloheximide) was added to cells after 3 h of nitrogen starvation. This loss of activity was not observed in the presence of cycloheximide alone. In a mutant yeast strain which lacks the nicotinamide adenine dinucleotide phosphate-dependent (anabolic) glutamate dehydrogenase, no significant decrease in amino acid transport was observed when ammonium sulfate was added to nitrogen-starved cells. A double mutant, which lacks the nicotinamide adenine dinucleotide phosphate-dependent enzyme and in addition has a depressed level of the nicotinamide adenine dinucleotide-dependent (catabolic) glutamate dehydrogenase, shows the same sensitivity to ammonium ion as the wild-type strain. These data suggest that the inhibition of amino acid transport by ammonium ion results from the uptake of this metabolite into the cell and its subsequent incorporation into the alpha-amino groups of glutamate and other amino acids.
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PMID:Inhibition of amino acid transport by ammonium ion in Saccharomyces cerevisiae. 24 Aug 6

A cyclic nucleotide-binding phosphohydrolase that possesses both a phosphomonoesterase and a phosphodiesterase catalytic function has been partially purified from Aspergillus nidulans. The enzyme hydrolyzes both p-nitrophenylphosphate and bis-(p-nitrophenyl)-phosphate. o'-Nucleoside monophosphates are the best physiological phosphomonesterase substrates but 5'- and 2'-nucleoside monophosphates are also hydrolyzed. The enzyme catalyzes the hydrolysis of adenosine 5'-triphosphate, adenosine 5'-diphosphate, and 2',3'- and 3'5'-cyclic nucleotides, but not of ribonucleic acid, deoxyribonucleic acid, or nicotinamide adenine dinucleotide. The enzyme has acid pH optima and is not activated by divalent cations. Nucleosides and nucleotides inhibit the enzyme. Cyclic nucleotides are competitive inhibitors of the phosphodiesterase-phosphomonoesterase. The enzyme can occur extracellularly. The phosphodiesterase-phosphomonoesterase is present at high levels in nitrogen-starved mycelium, and it is strongly repressed during growth in media containing ammonium or glutamine and weakly repressed during growth in glutamate-containing medium. Experiments with various area mutants show that this regulatory gene is involved in the control of the enzyme. No evidence for regulation of the enzyme by carbon or phosphorus starvation has been found.
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PMID:Enzymology and genetic regulation of a cyclic nucleotide-binding phosphodiesterase-phosphomonoesterase from Aspergillus nidulans. 24 43

The stability of tryptophan biosynthetic enzyme activities was examined in cultures of repressor-negative (trpR) strains of Escherichia coli K-12 incubated under conditions of nutrient starvation of chloramphenicol inhibition. The results show that four of the five activities examined are stable under most nongrowing conditions, whereas one activity, indoleglycerol phosphate (InGP) synthetase, carried by the trpC protein, is unstable under most conditions tested. Phosphoribosylanthranilate (PRA) isomerase activity, which is also carried by the trpC protein, is unstable during starvation for ammonium, cysteine, or sulfate but is stable under other nongrowing conditions where InGP synthetase is not. InGP synthetase activity but not PRA isomerase activity is also diminished about twofold in cultures using glycerol as a carbon-energy source. These results indicate that one or both activities of the trpC protein is specifically inactivated under several culture conditions. Experiments with antibodies to the trpC protein show that sulfate-starved and ammonium-starved cultures contain 20 to 40% less immunologically reactive trpC protein than unstarved cultures. This indicates that the trpC protein is probably partially degraded under these conditions. During recovery from sulfate starvation or ammonium starvation, cultures slowly regain normal levels of InGP synthetase and PRA isomerase activities, suggesting that inactivation may be reversible.
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PMID:Inactivation and partial degradation of phosphoribosylanthranilate isomerase-indoleglycerol phosphate synthetase in nongrowing cultures of Escherichia coli. 32 57

The effect of exogenous orthophosphate and mutations in regulatory genes of alkaline phosphatase on the level of nonspecific acid phosphatase was studied. The level of this enzyme as well as the level of alkaline phosphatase were shown to be regulated by exogenous orthophosphate being derepressed under phosphate starvation. The derepression of acid phosphatase is accompanied by more rapid secretion of enzyme from membranes to soluble fraction. Mutations in all the four regulatory genes decrease the level of enzyme in cells. Genes phoR and phoS, participating in regulation of alkaline phosphatase, are required for the derepression of acid phosphatase under the conditions of phosphate starvation.
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PMID:[Interrelationship between metabolic and genetic regulation of alkaline and acid phosphatases in E. coli cells]. 36 75

1. In yeast growing on ethanol a turnover rate of up to 2%/h was measured. As much as 80% of the protein was subject to turnover, and no marked heterogeneity in the rate of degradation of protein was observed. When the yeast grew on glucose, the protein was degraded at a lower rate (0.5-1%/h). 2. Starvation for a nitrogen source increased the rate of protein degradation severalfold, whereas deprivation of phosphate had only a marginal effect (30% increase). Removal of glucose from a medium containing 50mM-phosphate did not cause marked changes in the rate of protein degradation. In contrast, when the media were low in phosphate (0.1 mM) removal of glucose increased the rate of turnover 2-4-fold. 3. Protein degradation proceeded unimpaired when the intracellular concentration of ATP decreased from 4 to 1 mM, but stopped completely when it decreased below 0.3 mM.
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PMID:Effect of metabolic conditions on protein turnover in yeast. 37 19

The plasmid pMY3, which was constructed so as to express the Su+7 amber suppressor tRNA gene, also relaxes control of stable RNA synthesis in stringent cells. The relaxation is not growth medium or strain-dependent and does not occur in the presence of the vehicle alone. When expression of the effective sequence is diminished, in a lysogen of phi 80d3 ilv+Su+7, the sequence no longer affects RNA synthesis. The relaxation is general, extending to all or almost all tRNA loci, including tRNAs located in the ribosomal spacer regions, and to all ribosomal RNAs. Relaxed plasmid-carrying strains are still able to elevate guanosine tetra- and penta-phosphate levels in response to amino acid starvation, but steady state levels are somewhat diminished. Aminoacyl-tRNA falls to control levels when the plasmid-carrying strain is deprived of amino acid. Therefore, the relaxed strain perceives amino acid starvation, but does not respond normally. These properties define a novel locus which relaxes stringent control.
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PMID:Relaxation of stable RNA synthesis by a plasmid-borne locus. 37 46

We studied the effects of decreased aeration, chloramphenicol succinate, and 2,4-dinitrophenol on the cellular rates of glycogen synthesis and glucose utilization and on the cellular concentrations of adenine nucleotides, glucose 6-phosphate, fructose 1,6-diphosphate, and phosphoenolpyruvate during the first two periods of nitrogen starvation of Escherichia coli W4597(K). A quantitative relationship between the changes in the rates and the accompanying changes in the hexose phosphates is demonstrated. However, the relationship for glycogen synthesis is different in different sets of metabolic conditions. We suggest that this difference reflects a change in the steady state level of a previously unknown effector of ADP-glucose synthetase (glucose 1-phosphate adenylyltransferase, EC 2.7.7.27) the rate-limiting enzyme of bacterial glycogen synthesis. We show that the properties of the hypothetical in vivo effector are consistent with the inhibitory effects of ppGpp (guanosine 3'-diphosphate 5'-diphosphate) and pppGpp (guanosine 3'-diphosphate 5'-triphosphate) on this enzyme in vitro. In addition, tetracycline, an inhibitor of the synthesis of these nucleotides, apparently prevents the change in the quantitative relationship. The relationship between glucose utilization and the hexose phosphates is altered at the transition to Period II of nitrogen starvation. We propose that this change reflects the alteration of the cellular steady state level of an unknown effector of the glucose phosphotransferase system. In contrast to the ATP-hexose phosphate system of shared regulatory effects, the specific effects of the unknown effectors allow the rates of glucose utilization and glycogen synthesis to be altered independently of each other and independently of changes in the rate of glycolysis. This independence allows a greater latitude of response for the individual pathways in more severe metabolic stress or in accommodating the metabolic changes necessary for long term survival.
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PMID:Evidence for new factors in the coordinate regulation of energy metabolism in Escherichia coli. Effects of hypoxia, chloramphenicol succinate, and 2,4-dinitrophenol on glucose utilization, glycogen synthesis, adenylate energy charge, and hexose phosphates during the first two periods of nitrogen starvation. 38 3

A considerable amount of Mn2+-stimulated DNAase (deoxyribonuclease) activity is released by Bacillus subtilis 168 during sporulation in a glucose-deficient medium; much smaller amounts are released during starvation for phosphate or nitrogen. Protein synthesis is required. Two forms of evidence are presented that production of the DNAase is associated with events late in stage II of sporulation. 19 Thymidine starvation, which inhibits the biochemical events associated with sporulation, also inhibits release of the DNAase. 2. Several asporogenous mutants blocked at stage II or earlier and unable to produce alkaline phosphatase (a stage-II event) do not produce the enzyme. Mutants blocked towards the end of stage II or later produce both enzymes. During sporulation of the wild-type strain, the DNAase appears about 1 h after alkaline phosphatase. The results suggest that production of the DNAase is controlled by a still-undiscovered stage-II genetic locus.
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PMID:Extracellular manganese-stimulated deoxyribonuclease as a marker event in sporulation of Bacillus subtilis. 41 78


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