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

The steady state concentration of carbohydrate and adenosine phosphate metabolites in rat and rabbit liver and in rabbit skeletal muscle and oxidative phosphorylation parameters of rat and rabbit liver mitochondria were compared. The effects of 24 hr starvation on the energy metabolism of liver and skeletal muscle of the animals were investigated. The steady state concentrations of glycogen and phosphoenolpyruvate in normal rabbit liver were found to be much lower than in the rat and other mammalian livers (45.7 mumoles of glucose equivalents and 38 nmoles of PEP per 1 g of liver wet mass, respectively). On the contrast, the concentrations of glucose 6-phosphate, pyruvate and Pi in rabbit skeletal muscle were unusually high (up to 3, 1 and 15 mumoles per 1 g, respectively). In terms of glucose, pyruvate, lactate, Pi, adenine nucleotide contents and cytosolic NAD+/NADH ratio in the liver, and glycogen, glucose, lactate, creatine and adenosine phosphates in skeletal muscle and oxidative and phosphorylated properties of isolated liver mitochondria, no significant differences between rat and rabbit were found. During 24 hr starvation gluconeogenesis in rabbit liver occurred earlier and was more intensive than in rat liver. This is indicative of the existence of interspecies differences in the control mechanisms of carbohydrate and phosphorus metabolism.
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PMID:[Comparative study of energy metabolism in the liver and skeletal muscles of rat and rabbit. Effect of starvation]. 727 60

Glucose is essential for the energy metabolism of some cells and conservation of glucose is obligatory for survival during starvation. The principal site of this glucose conservation is the mitochondrial pyruvate dehydrogenase (PDH) complex, which is regulated by reversible phosphorylation (phosphorylation is inactivating). In cells in which glucose oxidation is switched off during starvation, fatty acids are used as fuel, and acetyl CoA and NADH formed by beta-oxidation promote phosphorylation of PDH complex by activation of PDH kinase. A longer-term mechanism further increases PDH kinase activity in response to cAMP and products of beta-oxidation of fatty acids. Coordinated inhibition of glycolytic flux mediated by effects of citrate on PFK1 and PFK2 in muscles and liver results in an associated inhibition of glucose uptake. Similar mechanisms lead to impaired glucose oxidation in diabetes.
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PMID:Glucose fatty acid interactions and the regulation of glucose disposal. 792 13

NADH dehydrogenase is the first component of the respiratory chain. It transfers electrons from NADH to ubiquinone and concomitantly establishes a proton motive force across the membrane. Salmonella typhimurium mutants defective in this enzyme were isolated in a screen for strains with increased expression of beta-galactosidase from a hemA-lacZ protein fusion. This unexpected phenotype results from stabilization of the hybrid protein during carbon starvation and is apparently due to an energy requirement for proteolytic attack. Sequence analysis of DNA fragments cloned from an insertion mutant indicates that S. typhimurium has a large cluster of genes encoding the energy-conserving NADH dehydrogenase, similar to one recently described in Paracoccus denitrificans. These findings establish the potential for genetic analysis of a complex enzyme whose function, especially in proton efflux, is poorly understood.
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PMID:Mutants defective in the energy-conserving NADH dehydrogenase of Salmonella typhimurium identified by a decrease in energy-dependent proteolysis after carbon starvation. 823 29

Under a limited set of hitherto incompletely defined conditions, inhibition of respiration has been shown to cause transient oscillations in NAD(P)H fluorescence of yeast cells. In this paper, we apply a new method [1992, Anal. Biochem. 204, 118-132] for extraction of intracellular metabolites. This method involves spraying the cells into -40 degrees C methanol; the neutral pH allows extraction of nearly all intracellular metabolites, including NADH. Close to the shift from glucose to ethanol as a growth substrate, the cells acquire a make-up amenable to sustained oscillations in intracellular concentrations of NADH and glycolytic intermediates such as glucose-6-phosphate. NADH was found to oscillate between 200 microM and 400 microM intracellular concentration. The cellular make-up determining the tendency to oscillate is 'remembered' by the cells after three hours of starvation.
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PMID:Around the growth phase transition S. cerevisiae's make-up favours sustained oscillations of intracellular metabolites. 843 31

Anaerobic metabolism of the simplest, best understood enteric bacteria such as Escherichia coli is unexpectedly complex. Recent studies of the biochemistry and genetics of nitrate reduction via nitrite to ammonia by enteric bacteria have provided insights into the reasons for this complexity. An NADH-dependent nitrite reductase in the cytoplasm works in partnership with the respiratory nitrate reductase on the cytoplasmic side of the membrane when nitrate is abundant. There is also an electrogenic, formate-dependent nitrite reductase ready to work in partnership with a periplasmic nitrate reductase when nitrite is available but nitrate is scarce. A third E. coli nitrate reductase, NarZYWV, and the poorly expressed formate dehydrogenase O possibly facilitate rapid adaptation to oxygen starvation pending the synthesis of the major respiratory formate-nitrate oxidoreductase. Although most anaerobically expressed genes are subject to transcription control, none of them are totally switched off. This enables the bacteria to be ready for a change in fortune: when growing anaerobically with nitrate, they can respond equally rapidly whether times get better with the arrival of oxygen, or get worse when the nitrate is depleted. Far from being redundant, the complexity is essential for survival in a changing environment.
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PMID:Nitrate reduction to ammonia by enteric bacteria: redundancy, or a strategy for survival during oxygen starvation? 891 48

In differentiated tissues, such as muscle and brain, increased adenosine monophosphate (AMP) levels stimulate glycolytic flux rates. In the breast cancer cell line MCF-7, which characteristically has a constantly high glycolytic flux rate, AMP induces a strong inhibition of glycolysis. The human breast cancer cell line MDA-MB-453, on the other hand, is characterized by a more differentiated metabolic phenotype. MDA-MB-453 cells have a lower glycolytic flux rate and higher pyruvate consumption than MCF-7 cells. In addition, they have an active glycerol 3-phosphate shuttle. AMP inhibits cell proliferation as well as NAD and NADH synthesis in both MCF-7 and MDA-MB-453 cells. However, in MDA-MB-453 cells glycolysis is slightly activated by AMP. This disparate response of glycolytic flux rate to AMP treatment is presumably caused by the fact that the reduced NAD and NADH levels in AMP-treated MDA-MB-453 cells reduce lactate dehydrogenase but not cytosolic glycerol-3-phosphate dehydrogenase reaction. Due to the different enzymatic complement in MCF-7 cells, proliferation is inhibited under glucose starvation, whereas MDA-MB-453 cells grow under these conditions. The inhibition of cell proliferation correlates with a reduction in glycolytic carbon flow to synthetic processes and a decrease in phosphotyrosine content of several proteins in both cell lines.
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PMID:Effect of extracellular AMP on cell proliferation and metabolism of breast cancer cell lines with high and low glycolytic rates. 903 May 54

The secretion of numerous proteins during vegetative growth of Myxococcus xanthus, and the multicellular development cycle induced upon starvation of these bacteria, are partially interrelated in so far as mutants impaired in extracellular protein production are unable to undergo development. We have cloned and sequenced a gene in which a Tn5 insertion leads to a decrease in the production of most, if not all, extracellular proteins, and prevents development and sporulation. The deduced protein is homologous to the putative ubiquinone-binding subunit of bacterial and mitochondrial NADH:ubiquinone oxidoreductases (complex I). This is the first example of the presence of this complex in a bacterium from subclass delta of the proteobacteria. This gene is expressed during growth and during early development. As its disruption by Tn5 does not impair growth of the mutant strain, we assume the presence of a second alternative NADH oxidoreductase, and suggest that the phenotypic alterations caused by the mutation are due to a decrease in the proton-motive force.
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PMID:A gene involved in both protein secretion during growth and starvation-induced development encodes a subunit of the NADH:ubiquinone oxidoreductase in Myxococcus xanthus. 907 40

The NADH-dependent Fe(3+)-chelate reductase (NFCHR) of tomato (Lycopersicon esculentum L.) roots, a strategy I species, was investigated. The Fe(3+)-citrate reductase (FeCitR) assay was strongly inhibited by p-hydroxymercuribenzoic acid (PHMB); moreover, the inhibitor was found to be more specific to the FeCitR assay than to the Fe(3+)-EDTA reductase assay, which was catalyzed by at least another reductase of 46 kDa. After high-speed centrifugation of tomato root membranes, high FeCitR activities were detected in pellets and lower activities in supernatants. After two-phase partitioning of microsomes, FeCitR activity (91 nmol.min-1.mg-1) was less active in the upper phase (plasma membrane) than in the lower phase (277 nmol.min-1.mg-1). However, only the activity of the plasma-membrane-associated NFCHR (FeCitR) was significantly enhanced (2.6-fold) in iron-deficient tomato plants, whereas that of NFCHR in non-plasma-membrane rich fractions was unaffected by this treatment. The NFCHR obtained from lysophosphatidylcholine-solubilized plasma membrane was present as a 200-kDa protein complex following fast protein liquid chromatography on Superdex 200, or as a 28-kDa form following Blue Sepharose CL-6B chromatography. Both preparations were more active following iron starvation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the 28-kDa protein purified from solubilized tomato microsomes or supernatant fractions by a final Mono Q step consisted of a single band of 32 kDa. Tomato root NFCHR resembled the NFCHR of maize (a strategy II plant, P Bagnaresi and P Pupillo, 1995, J Exp Bot 46: 1497-1503) in several properties: relative molecular mass, hydrophilicity, chromatographic behaviour, sensitivity to mercurials, specificity for electron donors and acceptors (e.g. cytochrome c), and a ferricyanide reductase-to-FeCitR ratio of 2.5. Preincubation with NADH partially protected NFCHR from PHMB-induced inactivation. Our data show that strategy I and II plants seem to share similar NFCHR proteins, which appear to belong to the cytochrome b5 reductase flavoprotein group.
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PMID:The NADH-dependent Fe(3+)-chelate reductases of tomato roots. 926 86

Four mitochondrial protein kinases have been cloned. These proteins represent a new family of protein kinases, related by sequence to the bacterial protein kinases but by function to the eukaryotic serine protein kinases. Arg288 is required for recognition by BCKDK of the phosphorylation site on the E1alpha subunit of the BCKDH complex. BCKDK inhibits the dehydrogenase activity of the BCKDH complex by introducing a negative charge into the active-site pocket of the E1 component. Protein starvation of rats induces an increase in the amount of BCKDK bound to the BCKDH complex. This causes inactivation of the BCKDH complex and conserves branched-chain amino acids for protein synthesis in the protein-starved state. Expression of the different PDK isoenzymes is tissue specific, and the different PDK isoenzymes are unique with respect to kinetic parameters for ATP and ADP and sensitivity to allosteric effectors (NADH, NAD+, coenzyme A, acetyl-CoA, pyruvate, and dichloroacetate). Preliminary experiments indicate that an increased amount of PDK2 protein partly explains the increase in PDK activity that occurs in rat liver in response to chemically induced diabetes.
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PMID:Mitochondrial alpha-ketoacid dehydrogenase kinases: a new family of protein kinases. 934 45

Hansenula polymorpha (syn. Pichia angusta) is able to grow on nitrate as sole nitrogen source. Nitrate reductase (NR) assays, optimized in crude extracts from nitrate-grown cells, revealed that NR preferentially used NADPH, but also used NADH, as electron donor and required FAD for maximum activity. NR activity was present in nitrate-grown and nitrite-grown cells, and was absent in cells grown in ammonium, glutamate and methylamine. Addition of reduced nitrogen compounds to nitrate-grown cells led to loss of NR activity, even if added with nitrate. Under nitrogen starvation, NR activity was not observed; however, following growth on nitrate, NR activity is maintained in the absence of nitrate. Increases but not decreases in NR activity were dependent on protein synthesis. Conditions for chlorate selection were optimized, and Nit- (nitrate-) mutants were isolated. Some of these mutants showed reduced or absent NR activity. Sixty-one NR- mutants revealed the monogenic recessive nature of their lesions and were grouped in 10 complementation classes. These mutants will be used in gene cloning experiments aimed at identifying structural and regulatory elements involved in the first step of nitrate reduction.
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PMID:Nitrate reduction and the isolation of Nit- mutants in Hansenula polymorpha. 972 55


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