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

Mitochondrial NAD-dependent (IDH) and cytosolic NADP-dependent isocitrate dehydrogenases have been considered as candidates for the production of 2-oxoglutarate required by the glutamine synthetase/glutamate synthase cycle. The increase in IDH transcripts in leaf and root tissues, induced by nitrate or NH4+ resupply to short-term N-starved tobacco (Nicotiana tabacum) plants, suggested that this enzyme could play such a role. The leaf and root steady-state mRNA levels of citrate synthase, acotinase, IDH, and glutamine synthetase were found to respond similarly to nitrate, whereas those for cytosolic NADP-dependent isocitrate dehydrogenase and fumarase responded differently. This apparent coordination occurred only at the mRNA level, since activity and protein levels of certain corresponding enzymes were not altered. Roots and leaves were not affected to the same extent either by N starvation or nitrate addition, the roots showing smaller changes in N metabolite levels. After nitrate resupply, these organs showed different response kinetics with respect to mRNA and N metabolite levels, suggesting that under such conditions nitrate assimilation was preferentially carried out in the roots. The differential effects appeared to reflect the C/N status after N starvation, the response kinetics being associated with the nitrate assimilatory capacity of each organ, signaled either by nitrate status or by metabolite(s) associated with its metabolism.
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PMID:Simultaneous expression of NAD-dependent isocitrate dehydrogenase and other krebs cycle genes after nitrate resupply to short-term nitrogen-starved tobacco 1039 6

It has been suggested that Escherichia coli can resist aerobic, glucose-starvation conditions by switching rapidly from an aerobic to a fermentative metabolism, thereby preventing the production by the respiratory chain of reactive oxygen species (ROS) that can damage cellular constituents. In contrast, it has been reported that E. coli cannot resist aerobic, phosphate (Pi)-starvation conditions, probably because of the maintenance of an aerobic metabolism and the continuous production of ROS. This paper presents evidence that E. coli cells starved for Pi under aerobic conditions indeed maintain an active aerobic metabolism for about 3 d, which allows the complete degradation of exogenous nutrients such as arginine (metabolized probably to putrescine via the SpeA-initiated pathway) and glucose (metabolized notably to acetate), but cell viability is not significantly affected because of the protection afforded against ROS through the expression of the RpoS and LexA regulons. The involvement of the LexA-controlled RuvAB and RecA proteins with the RecG and RecBCD proteins in metabolism and cell viability implies that DNA double-strand breaks (DSB), and thus hydroxyl radicals that normally generate this type of damage, are produced in Pi-starved cells. It is shown that induction of the LexA regulon, which helps protect Pi-starved cells, is totally prevented by introduction of a recB mutation, which indicates that DSB are actually the main DNA lesion generated in Pi-starved cells. The requirement of RpoS for survival of cells starved for Pi may thus be explained by the role played by various RpoS-controlled gene products such as KatE, KatG and Dps in the protection of DNA against ROS. In the same light, the degradation of arginine and threonine may be accounted for by the synthesis of polyamines (putrescine and spermidine) that protect nucleic acids from ROS. Besides LexA and RpoS, a third global regulator, the nucleoid-associated protein H-NS, is also shown to play a key role in Pi-starved cells. Through a modulation of the metabolism during Pi starvation, H-NS may perform two complementary tasks: it helps maintain a rapid metabolism of glucose and arginine, probably by favouring the activity of aerobic enzymes such as the NAD-dependent pyruvate dehydrogenase complex, and it may enhance the cellular defences against ROS which are then produced by increasing RpoS activity via the synthesis of acetate and presumably homoserine lactone.
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PMID:Role of Escherichia coli RpoS, LexA and H-NS global regulators in metabolism and survival under aerobic, phosphate-starvation conditions. 1043 94

The Escherichia coli ssuEADCB gene cluster is required for the utilization of alkanesulfonates as sulfur sources, and is expressed under conditions of sulfate or cysteine starvation. The SsuD and SsuE proteins were overexpressed and characterized. SsuE was purified to homogeneity as an N-terminal histidine-tagged fusion protein. Native SsuE was a homodimeric enzyme of M(r) 58,400, which catalyzed an NAD(P)H-dependent reduction of FMN, but it was also able to reduce FAD or riboflavin. The SsuD protein was purified to >98% purity using cation exchange, anion exchange, and hydrophobic interaction chromatography. The pure enzyme catalyzed the conversion of pentanesulfonic acid to sulfite and pentaldehyde and was able to desulfonate a wide range of sulfonated substrates including C-2 to C-10 unsubstituted linear alkanesulfonates, substituted ethanesulfonic acids and sulfonated buffers. SsuD catalysis was absolutely dependent on FMNH(2) and oxygen, and was maximal for SsuE/SsuD molar ratios of 2.1 to 4.2 in 10 mM Tris-HCl, pH 9.1. Native SsuD was a homotetrameric enzyme of M(r) 181,000. These results demonstrate that SsuD is a broad range FMNH(2)-dependent monooxygenase catalyzing the oxygenolytic conversion of alkanesulfonates to sulfite and the corresponding aldehydes. SsuE is the FMN reducing enzyme providing SsuD with FMNH(2).
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PMID:Characterization of a two-component alkanesulfonate monooxygenase from Escherichia coli. 1048 Aug 65

The metabolic responses occurring in cucumber (Cucumis sativus L.) roots (a strategy-I plant) grown under iron-deficiency conditions were studied in-vivo using 31P-nuclear magnetic resonance spectroscopy. Iron starvation induced activation of metabolism leading to the consumption of stored carbohydrates to produce the NAD(P)H, ATP and phosphoenolpyruvate necessary to sustain the increased activity of the NAD(P)H:Fe(3+)-reductase, the H(+)-ATPase (EC 3.6.1.35) and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Activation of catabolic pathways was supported by the enhancement of glycolytic enzymes and concentrations of the metabolites glucose-6-phosphate and fructose-6-phosphate, and by enhancement of the respiration rate. Moreover, Fe-deficiency induced a slight increase in the cytoplasmic (pHc) and vacuolar (pHv) pHs as well as a dramatic decrease in the vacuolar phosphate (Pi) concentration. A comparison was done using fusicoccin (FC), a fungal toxin which stimulates proton extrusion. Changes in pHc and pHv were measured after addition of FC. Under these conditions, a dramatic alkalinization of the pHv of -Fe roots was observed, as well as a concomitant Pi movement from the vacuole to the cytoplasm. These results showed that Fe starvation was indeed accompanied by the activation of metabolic processes useful for sustaining the typical responses occurring at the plasma-membrane level (i.e. increases in the NAD(P)H:Fe(3+)-reductase and H(+)-ATPase activities) as well as those involved in the homeostasis of pHc. The decrease in vacuolar Pi levels induced by Fe-deficiency and FC and movement of Pi from the vacuole to the cytoplasm suggest a possible involvement of this compound in the cellular pH-stat system.
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PMID:Metabolic responses in cucumber (Cucumis sativus L.) roots under Fe-deficiency: a 31P-nuclear magnetic resonance in-vivo study. 1087 32

For a number of organisms, the ability to withstand periods of nutrient deprivation correlates directly with lifespan. However, the underlying molecular mechanisms are poorly understood. We show that deletion of the N-myristoylprotein, Sip2p, reduces resistance to nutrient deprivation and shortens lifespan in Saccharomyces cerevisiae. This reduced lifespan is due to accelerated aging, as defined by loss of silencing from telomeres and mating loci, nucleolar fragmentation, and accumulation of extrachromosomal rDNA. Genetic studies indicate that sip2Delta produces its effect on aging by increasing the activity of Snf1p, a serine/threonine kinase involved in regulating global cellular responses to glucose starvation. Biochemical analyses reveal that as yeast age, hexokinase activity increases as does cellular ATP and NAD(+) content. The change in glucose metabolism represents a new correlate of aging in yeast and occurs to a greater degree, and at earlier generational ages in sip2Delta cells. Sip2p and Snf1p provide new molecular links between the regulation of cellular energy utilization and aging.
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PMID:Sip2p and its partner snf1p kinase affect aging in S. cerevisiae. 1092 2

The three Synechocystis PCC6803 genes homologous to proteobacterial Calvin cycle regulators (cbbR) have been analysed. sll0998 appeared to be crucial to cell viability, whereas both sll0030 and sll1594 were found to be dispensable for cell growth. In spite of their sequence homology, Sll0030 and Sll1594 did not appear to regulate the transcription of Calvin cycle key genes. Further analysis of Sll1594 showed that this protein plays an important role in the adaptation to inorganic carbon starvation and osmotic stress. Sll1594 mediates the response to these stress conditions by regulating the transcription of a new regulon including the monocistronic genes sll1594 and slr1727 (encoding a presumptive Na+/H+ antiporter), as well as the ndh3 operon encoding the NAD(P)H-dehydrogenase subunits F3 and D3 and a protein of unknown function. The sll1594 gene and the ndh3 operon are negatively controlled by Sll1594, which also regulates the expression of the slr1727 gene. Sequence alignment of the diverse Sll1594 DNA binding sites led us to propose the TCAATG-(N10)-ATCAAT sequence as the consensus motif. To our knowledge, this is the first report on the characterization and analysis of a transcriptional regulator for ndh genes in a photoautotrophic organism.
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PMID:Characterization and analysis of an NAD(P)H dehydrogenase transcriptional regulator critical for the survival of cyanobacteria facing inorganic carbon starvation and osmotic stress. 1113 65

In Aspergillus nidulans there are three NAD(+)-dependent alcohol dehydrogenases (ADHs) that are capable of utilizing ethanol as a substrate. ADHI is the physiological enzyme of ethanol catabolism and ADHIII is induced under conditions of anaerobiosis. The physiological role of ADHII (structural gene alcB) is unknown. We have measured beta-galactosidase in a transformant with an alcB::lacZ fusion and have shown that alcB is maximally expressed under conditions of carbon starvation. The behavior of the alcB::lacZ transformant suggests a hierarchy of repressing carbon sources characteristic of repression by the general carbon catabolite repressor protein, CreA, but in a creA(d)30 background the transformant shows only partial derepression of beta-galactosidase on 1% glucose compared to the creA+ strain. Our results suggest that, in addition to carbon catabolite repression acting via CreA, a CreA-independent mechanism is involved in induction of alcB on carbon starvation.
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PMID:ADHII in Aspergillus nidulans is induced by carbon starvation stress. 1127 24

Cytosolic redox balance has to be maintained in order to allow an enduring cellular metabolism. In other words, NADH generated in the cytosol has to be re-oxidized back to NAD(+). Aerobically this can be done by respiratory oxidation of cytosolic NADH. However, NADH is unable to cross the mitochondrial inner membrane and mechanisms are required for conveying cytosolic NADH to the mitochondrial electron transport chain. At least two such systems have proved to be functional in S. cerevisiae, the external NADH dehydrogenase (Luttik et al., 1998; Small and McAlister-Henn, 1998) and the G3P shuttle (Larsson et al., 1998). The aim of this investigation was to study the regulation and performance of these two systems in a wild-type strain of S. cerevisiae using aerobic glucose- and nitrogen-limited chemostat cultures. The rate of cytosolic NADH formation was calculated and as expected there was a continuous increase with increasing dilution rate. However, measurements of enzyme activities and respiratory activity on isolated mitochondria revealed a diminishing capacity at elevated dilution rates for both the external NADH dehydrogenase and the G3P shuttle. This suggests that adjustment of in vivo activities of these systems to proper levels is not achieved by changes in amount of protein but rather by, for example, activation/inhibition of existing enzymes. Adenine nucleotides are well-known allosteric regulators and both the external NADH and the G3P shuttle were sensitive to inhibition by ATP. The most severe inhibition was probably on the G3P shuttle, since one of its member proteins, Gpdp, turned out to be exceptionally sensitive to ATP. The external NADH dehydrogenase is suggested as the main system employed for oxidation of cytosolic NADH. The G3P shuttle is proposed to be of some importance at low growth rates and perhaps its real significance is only expressed during starvation conditions.
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PMID:Cytosolic redox metabolism in aerobic chemostat cultures of Saccharomyces cerevisiae. 1132 72

Embryo axes isolated from germinating lupine seeds were cultivated in vitro for 24-96 h over media containing either 60 mmol/L sucrose or no sucrose. Ultrastructural studies showed that large vacuoles were accumulating in a central region of primary parenchyma cells in sucrose starved lupine embryo axes, whereas cytoplasm along with organelles were forced to a periphery of the cells. We suggest that the autolysis of cytoplasmic proteins contributes to the accumulation of the vacuoles and this suggestion is consistent with the results of the characterisation of protein content. The level of cytosolic proteins was reduced by 50% and the activity of cytosolic marker enzyme, PEP carboxylase, was reduced by 46% in starved embryos as compared to control. The mitochondria from starved tissues were not degraded. The level of mitochondrial proteins was reduced by only 10% and the activity of mitochondrial NAD-isocitrate dehydrogenase decreased by 8% as a result of starvation. As demonstrated by the results of Percoll density gradient centrifugation, sucrose starvation caused an increase of 49% in many of the higher density mitochondria fractions, whereas many of the lower density mitochondria fractions were decreased by 33%. The samples of mitochondria from starved embryo axes were determined to have higher respiration activity in the presence of glutamate and malate as compared to control samples. EPR-based analyses of free radicals showed the presence of free radicals with a signal at g = 2.0060 in embryo axes. The level of the radical was two times higher in sucrose-starved embryo axes than in control (the level of this radical increased in senescing plant tissues as well). The results of EPR-based quantitation of Mn2+ ions revealed that the level was a few times higher in starved material than in control. Starved embryo axes, however, do possess a number of adaptive mechanisms protecting them from oxidative damage. Densitometric analyses of gels revealed an increase in the activity of SOD in sugar-starved embryos, whereas CAT and POX activities were lower in axes grown without sucrose as compared to control. Superoxide dismutase, catalase and peroxidase zymogram analyses showed that synthesis of new isoforms was not induced by sugar starvation. An accumulation of phytoferritin was found in plastids of sucrose starved embryos. These results are discussed in relation to the metabolic changes observed in senescing plant tissues.
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PMID:Metabolic and ultrastructural responses of lupine embryo axes to sugar starvation. 1274 88

Specimens of the fruit beetle Pachnoda sinuata were starved for up to 30 days. The weight of the beetles declined consistently throughout the starvation period. Concentrations of carbohydrates and alanine in flight muscles, fat body and haemolymph decreased rapidly after onset of starvation, while the concentration of proline remained high. Whereas the lipid concentrations in the haemolymph did not change significantly upon starvation, the lipid content in flight muscles and fat body decreased significantly.Beetles that had been starved for 14 days responded to injection of Mem-CC, the endogenous neuropeptide from its corpora cardiaca, with hyperprolinaemia and a decrease in the alanine level, but no such effect was monitored after prolonged starvation of 28 days. Regardless of the period of starvation, Mem-CC injection could not cause hypertrehalosaemia or hyperlipaemia, although carbohydrates were increased in fed beetles after injection.Flight ability of beetles that had been starved for 15 or 30 days was apparently not impaired. During such periods, beetles used proline exclusively as fuel for flight as evidenced by the increase in the level of alanine in the haemolymph and decrease of the level of proline; the concentrations of carbohydrates and lipids remained unchanged.Activities of malic enzyme and alanine aminotransferase (enzymes involved in transamination in proline metabolism), glyceraldehyde-3-phosphate dehydrogenase (enzyme of glycolysis), 3-hydroxyacyl-CoA dehydrogenase (enzyme of beta-oxidation of fatty acids) and of malate dehydrogenase (enzyme of Krebs cycle) were measured in fat body and flight muscles. In flight muscle tissue the maximum activity of NAD(+)-dependent malic enzyme increased, while that of glyceraldehyde-3-phosphate dehydrogenase decreased during starvation, and malate dehydrogenase, 3-hydroxyacyl-CoA dehydrogenase and alanine aminotransferase were unchanged. In fat body tissue, activities of NADP(+)-dependent malic enzyme and 3-hydroxyacyl-CoA dehydrogenase increased during food deprivation and activities of glyceraldehyde-3-phosphate dehydrogenase, malate dehydrogenase and alanine aminotransferase remained unchanged.
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PMID:Metabolic changes in the African fruit beetle, Pachnoda sinuata, during starvation. 1277 Feb 39


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