Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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

Production of glutamine synthetase in Saccharomyces cerevisiae is controlled by three regulatory systems. One system responds to glutamine levels and depends on the positively acting GLN3 product. This system mediates derepression of glutamine synthetase in response to pyrimidine limitation as well, but genetic evidence argues that this is an indirect effect of depletion of the glutamine pool. The second system is general amino acid control, which couples derepression of a variety of biosynthetic enzymes to starvation for many single amino acids. This system operates through the positive regulatory element GCN4. Expression of histidinol dehydrogenase, which is under general control, is not stimulated by glutamine limitation. A third system responds to purine limitation. No specific regulatory element has been identified, but depression of glutamine synthetase is observed during purine starvation in gln3 gcn4 double mutants. This demonstrates that a separate purine regulatory element must exist. Pulse-labeling and immunoprecipitation experiments indicate that all three systems control glutamine synthetase at the level of subunit synthesis.
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PMID:Three regulatory systems control production of glutamine synthetase in Saccharomyces cerevisiae. 615 13

Glutamate synthase catalyzes glutamate formation from 2-oxoglutarate plus glutamine and plays an essential role when glutamate biosynthesis by glutamate dehydrogenase is not possible. Glutamate synthase activity has been determined in a number of Neurospora crassa mutant strains with various defects in nitrogen metabolism. Of particular interest were two mutants phenotypically mute except in an am (biosynthetic nicotinamide adenine dinucleotide phosphate-glutamate dehydrogenase deficient, glutamate requiring) background. These mutants, i and en-am, are so-called enhancers of am; they have been redesignated herein as en(am)-1 and en(am)-2, respectively. Although glutamate synthase levels in en(am)-1 were essentially wild type, the en(am)-2 strain was devoid of glutamate synthase activity under all conditions examined, suggesting that en(am)-2 may be the structural locus for glutamate synthase. Regulation of glutamate synthase occurred to some extent, presumably in response to glutamate requirements. Glutamate starvation, as in am mutants, led to enhanced activity. In contrast, glutamine limitation, as in gln-1 mutants, depressed glutamate synthase levels.
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PMID:Glutamate synthase levels in Neurospora crassa mutants altered with respect to nitrogen metabolism. 615 51

Rates of de novo and salvage purine synthesis decrease by approximately 80 and 60%, respectively, when normal human lymphoblasts are starved 3 h for an essential amino acid (Boss, G. R., and Erbe, R. W. (1982) J. Biol. Chem. 257, 4242-4247). Amino acid starvation decreased the intracellular phosphoribosylpyrophosphate (PP-Rib-P) and ribose 5-phosphate concentrations by approximately 40%, but neither the specific activities of PP-Rib-P synthetase and glutamine amidophosphoribosyltransferase nor the intracellular concentrations of purine nucleotides and inorganic phosphate changed significantly. In mutant cells with either an increased capacity to generate PP-Rib-P (superactive PP-Rib-P synthetase), or an increased PP-Rib-P concentration (inosinate-guanylate:pyrophosphate phosphoribosyltransferase deficiency), the intracellular PP-Rib-P concentration decreased by less than 15% during amino acid starvation and de novo purine synthesis decreased significantly less than in normal cells. When normal cells were treated with drugs that simultaneously decreased feed-back inhibition by purine nucleotides and increased the intracellular concentration of ribose 5-phosphate and PP-Rib-P rates of de novo purine synthesis were stimulated 3-fold in nonstarved cells and more than 8-fold in starved cells. This greater stimulation in the starved cells appeared to be from the increased PP-Rib-P production; moreover, in starved cells in which the increase of the PP-Rib-P concentration by the drugs was impaired because of purine nucleoside phosphorylase deficiency, rates of de novo purine synthesis increased only 3.5-fold. The data suggest that amino acid starvation decreases purine synthesis by decreasing the generation of PP-Rib-P from glucose.
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PMID:Decreased phosphoribosylpyrophosphate as the basis for decreased purine synthesis during amino acid starvation of human lymphoblasts. 619 53

Nitrogen starvation has been shown to increase the cytosolic arginine concentration and to accelerate protein turnover in mycelia of Neurospora crassa. The cytosolic arginine is derived from a metabolically inactive vacuolar pool. Redistribution of arginine between cytosolic and vacuolar compartments is the result of mobilization of this metabolite in response to nitrogen starvation. Mobilization of arginine (and purines) also occurred in response to glutamine limitation, but arginine accumulated upon proline starvation. These observations indicate that mobilization is a consequence of glutamine limitation rather than a general response to amino acid starvation (or limitation). Analysis of the amino acid pools in mycelia subjected to starvation or limitation suggests that glutamine (or a metabolite derived from glutamine) provides a signal which determines the metabolic fate of vacuolar arginine. The results are consistent with the hypothesis that vacuolar compartmentation provides a readily available store of nitrogen-rich compounds to be utilized during differentiation or under conditions of nutritional stress.
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PMID:Mobilization of vacuolar arginine in Neurospora crassa. Mechanism and role of glutamine. 623 20

Regulation of hexose transport in NIL hamster fibroblasts has been studied in confluent cultures preconditioned for 24 hr in media deprived of glutamine or of serum or of both. Cultures maintained in media containing dialyzed fetal calf serum and 4 mM glutamine accumulated up to 72 nmol of glutamine per mg of cell protein; in contrast, cells deprived of glutamine contained less than 1 nmol/mg of cell protein. Glutamine elicited a general enhancement of hexose transport compared with transport in glutamine-deprived cultures. This enhancement was particularly pronounced in glucose-fed cultures which in the absence of glutamine showed conspicuously low transport activity. When maintained in glucose media, cultures deprived of serum also showed a marked loss of hexose transport which, in this case, was not compensated for by addition of glutamine. However, regardless of the presence or absence of glutamine, these cultures were able to develop the usual transport enhancement response to glucose starvation. Moreover, 2,4-dinitrophenol was also able to elicit a pronounced enhancement of hexose transport in the glucose-fed cultures; this effect surpassed even the transport derepression observed in the glucose-starved cultures. In polyoma-transformed cultures maintained in serum-free media, hexose transport remained relatively high, even in the presence of glucose. However, addition of glutamine brought about an enhancement in both the presence and absence of serum. The various phenomena are discussed in regard to protein turnover in general and more specifically the turnover of hexose transport carriers.
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PMID:Effects of combined glutamine and serum deprivation on glucose control of hexose transport in mammalian fibroblast cultures. 625 70

The behavior of the activities of GMP synthetase (xanthosine-5'-phosphate: L-glutamine amino-ligase(AMP-forming),EC 6.3.5.2) and GMP kinase (ATP: (d)GMP phosphotransferase,EC 2.7.4.8) was elucidated in cytosol preparations of rat tissues, including fetal, neonatal and regenerating liver, in a transplantable kidney tumor, and in a spectrum of 11 hepatomas of different growth rates. GMP kinase activity was 60-fold or more higher than GMP synthetase activity in all of the examined tissues. GMP synthetase activity was increased in all hepatomas and in the kidney tumor, compared to control tissues, reaching 5.5-fold the normal liver values in the most rapidly growing hepatoma. This increase correlated with the tumor growth rates. GMP kinase activity showed no consistent pattern of alteration in the tumors. In both fetal and neonatal rat liver the activity of GMP synthetase was 2.5-times higher than in livers of adult rats, but GMP kinase activity did not change markedly during liver development. After partial hepatectomy GMP synthetase activity was elevated, reaching a peak of 155% of the sham-operated control values by 36 h after the operation. GMP kinase activity was not affected by partial hepatectomy. After 3 days starvation hepatic GMP kinase activity decreased slightly faster than total cytosol protein, while GMP synthetase activity was preferentially maintained. These results indicate that GMP synthetase activity was linked with cellular proliferation in differentiating, regenerating and neoplastic tissues.
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PMID:Guanosine-5'-phosphate synthetase and guanosine-5'-phosphate kinase in rat hepatomas and kidney tumors. 626 Feb 5

The distribution of lipid-linked oligosaccharide intermediates in cultured mammalian cells has been studied under conditions of glucose deprivation. It was found that at low to moderate cell densities within 20 min of glucose starvation, the major species of lipid-linked oligosaccharide shifted from mainly a single species containing three glucose, nine mannose, and two N-acetylglucosamine residues to a pattern dominated by two species containing either five mannose and two N-acetylglucosamine residues or two mannose and two N-acetylglucosamine residues. At high cell densities, this effect was not evident. Continued glucose starvation at low density resulted in a second shift in distribution in which the proportions of these two species decreased and that of the original major species (Glc3Man9GlcNAc2) increased. Addition of glucose or mannose, but not pyruvate, glutamine, galactose, inositol, or glycine, prevented the shift to the Man5GlcNAc2 and Man2GlcNAc2 species. The intermediates that accumulate during glucose starvation were identified by their elution position on gel filtration columns, sensitivity to digestion with alpha-mannosidase, resistance to digestion with endo-beta-N-acetylglucosaminidase H, and by the products of Smith degradation. These data suggest that a regulatory point in the lipid-linked oligosaccharide synthetic pathway exists at the reaction in which Man5GlcNAc2-P-P-dolichol is converted to Man6GlcNAc2-P-P-dolichol.
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PMID:Transitory effects of glucose starvation on the synthesis of dolichol-linked oligosaccharides in mammalian cells. 626 25

The uptake of nutrients (glucose, glutamine, and N-acetylglucosamine), the intracellular concentrations of metabolites (glucose-6-phosphate, cyclic AMP, amino acids, trehalose, and glycogen) and cell wall composition were studied in Candida albicans. These analyses were carried out with exponential-phase, stationary-phase, and starved yeast cells, and during germ-tube formation. Germ tubes formed during a 3-h incubation of starved yeast cells (0.8 X 10(8) cells/mL) at 37 degrees C during which time the nutrients glucose plus glutamine or N-acetylglucosamine (2.5 mM of each) were completely utilized. Control incubations with these nutrients at 28 degrees C did not form germ tubes. Uptake of N-acetylglucosamine and glutamine was inhibited by cycloheximide which suggests that de novo protein synthesis was required for the induction of these uptake systems. The glucose-6-phosphate content varied from 0.4 nmol/mg dry weight for starved cells to 2-3 nmol/mg dry weight for growing yeast cells and germ tube forming cells. Trehalose content varied from 85 nmol/mg dry weight (growing yeast cells and germ tube forming cells) to 165 nmol/mg weight (stationary-phase cells). The glycogen content decreased during germ-tube formation (from 800 to 600 nmol glucose equivalent/mg dry weight) but increased (to 1000 nmol glucose equivalent/mg dry weight) in the control incubation of yeast cells. Cyclic AMP remained constant throughout germ-tube formation at 4-6 pmol/mg dry weight. The total amino acid pool was similar in exponential, starved, and germ tube forming cells but there were changes in the amounts of individual amino acids. The overall cell wall composition of yeast cells and germ tube forming cells were similar: lipid (2%, w/w); protein (3-6%), and carbohydrate (77-85%). The total carbohydrates were accounted for as the following fractions: alkali-soluble glucan (3-8%), mannan (20-23%), acid-soluble glucan (24-27%), and acid-insoluble glucan (18-26%). The relative amounts of the alkali-soluble and insoluble glucan changed during starvation of yeast cells, reinitiation of yeast-phase growth, and germ-tube formation. Analysis of the insoluble glucan fraction from cells labelled with [14C]glucose during germ-tube formation showed that the chitin content of the cell wall increased from 0.6% to 2.7% (w/w).
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PMID:An analysis of the metabolism and cell wall composition of Candida albicans during germ-tube formation. 632 47

In order to elucidate further the effects of starvation on islet metabolism and insulin release, pancreatic islets of mice were isolated and incubated in the presence of various nutrient secretagogues. Starvation for 60 h completely blocked the insulin release in response to either 16.7 mM glucose or 10 mM leucine. The further addition of 20 mM adenosine partly restored the insulin response. Glucose, adenosine, glucose + adenosine, glucose + leucine or leucine + adenosine all increased the NADH/NAD ratios over basal values in islets from both fed and starved mice. No effects of starvation were observed on islet NADH/NAD ratios in any of the above media, but when islets of starved animals were incubated in the absence of any metabolic substrates the NADH/NAD ratios were decreased. In the absence of exogenous substrates the respiratory rate was also lower in islets from starved animals. Respiratory stimulation evoked by either 16.7 mM glucose or 10 mM leucine + 10 mM glutamine was lower after starvation, whereas glucose + adenosine, glucose + leucine and adenosine all induced normal respiratory responses. No differences between the 45Ca2+ uptake of islets from either starved or fed mice were observed under any conditions. It is concluded that, in starvation, a dissociation between islet insulin release and metabolism (measured as NADH/NAD ratios, oxygen consumption and 45Ca2+ uptake) may exist in the presence of certain nutrient secretagogues.
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PMID:Effects of glucose, leucine and adenosine on insulin release, 45Ca2+ net uptake, NADH/NAD ratios and oxygen consumption of islets isolated from fed and starved mice. 634 Nov 17

The effects of dietary protein level, exogenous insulin and starvation on amino acid (AA) uptake or release from the hindquarters of steers were studied. Irrespective of diet fed, physiologic state or time after feeding there was a net release of alanine and glutamine from hind limbs of steers. Steers from control 1 exhibited a net release of leucine, valine and isoleucine (branched-chain amino acids, BCAA) in the postabsorptive (prefeeding) state, but steers from control group 2 exhibited some BCAA uptake by the hind limb. At 2 and 4 hours postfeeding, there was marked net uptake by hind limbs of BCAA and total AA in steers fed the control (12.8% protein) diets. At 2 and 4 hours after feeding there was slight hind-limb uptake of BCAA and total AA in steers fed the low protein diet, while there was a massive uptake of BCAA and total AA by hind limbs of steers fed the high protein diet. Upon insulin injection to postabsorptive steers, BCAA and total AA uptake by hind limbs was markedly stimulated at 1 and 2 hours, but by 4 hours the AA flux pattern had reverted to that in the postabsorptive state. After 24 and 48 hours of starvation, steer hindquarters released significant quantities of BCAA, essential amino acids and total amino acids.
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PMID:Effect of nutritional state and insulin on hind-limb amino acid metabolism in steers. 634 21


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