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

The importance of the ectomycorrhiza symbiosis for plant acquisition of phosphorus and nitrogen is well established whereas its contribution to sulfur nutrition is only marginally understood. In a first step to investigate the role of ectomycorrhiza in plant sulfur nutrition, we characterized sulfate and glutathione uptake in Laccaria bicolor. By studying the regulation of sulfate uptake in this ectomycorrhizal fungus, we found that in contrast to bacteria, yeast, and plants, sulfate uptake in L. bicolor was not feedback-inhibited by glutathione. On the other hand, sulfate uptake was increased by sulfur starvation as in other organisms. The activity of 3'-phosphoadenosine 5'-phosphosulfate reductase, the key enzyme of the assimilatory sulfate reduction pathway in fungi, was increased by sulfur starvation and decreased after treatment with glutathione revealing an uncoupling of sulfate uptake and reduction in the presence of reduced sulfur compounds. These results support the hypothesis that L. bicolor increases sulfate supply to the plant by extended sulfate uptake and the plant provides the ectomycorrhizal fungus with reduced sulfur.
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PMID:Sulfur uptake in the ectomycorrhizal fungus Laccaria bicolor S238N. 1659 84

Lignocellulosic biomass, rich in hexose and pentose sugars, is an attractive resource for commercially viable bioethanol production. Saccharomyces cerevisiae efficiently ferments hexoses but is naturally unable to utilize pentoses. Metabolic engineering of this yeast has resulted in strains capable of xylose utilization. However, even the best recombinant S. cerevisiae strains of today metabolize xylose with a low rate compared to glucose. This study compares the transcript profiles of an S. cerevisiae strain engineered to utilize xylose via the xylose reductase-xylitol dehydrogenase pathway in aerobic chemostat cultures with glucose or xylose as the main carbon source. Compared to the glucose culture, 125 genes were upregulated, whereas 100 genes were downregulated in the xylose culture. A number of genes encoding enzymes capable of nicotinamide adenine dinucleotide phosphate regeneration were upregulated in the xylose culture. Furthermore, xylose provoked increased activities of the pathways of acetyl-CoA synthesis and sterol biosynthesis. Notably, our results suggest that cells metabolizing xylose are not in a completely repressed or in a derepressed state either, indicating that xylose was recognized neither as a fermentable nor as a respirative carbon source. In addition, a considerable number of the changes observed in the gene expression between glucose and xylose samples were closely related to the starvation response.
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PMID:Transcription analysis of recombinant saccharomyces cerevisiae reveals novel responses to xylose. 1663 84

3Beta-hydroxysterol Delta(14)-reductase operates during the conversion of lanosterol to cholesterol in mammalian cells. Besides the endoplasmic reticulum 3beta-hydroxysterol Delta(14)-reductase (C14SR) encoded by TM7SF2 gene, the lamin B receptor (LBR) of the inner nuclear membrane possesses 3beta-hydroxysterol Delta(14)-reductase activity, based on its ability to complement C14SR-defective yeast strains. LBR was indicated as the primary 3beta-hydroxysterol Delta(14)-reductase in human cholesterol biosynthesis, since mutations in LBR gene were found in Greenberg skeletal dysplasia, characterized by accumulation of Delta(14)-unsaturated sterols. This study addresses the issue of C14SR and LBR role in cholesterol biosynthesis. Both human C14SR and LBR expressed in COS-1 cells exhibit 3beta-hydroxysterol Delta(14)-reductase activity in vitro. TM7SF2 mRNA and C14SR protein expression in HepG2 cells grown in delipidated serum (LPDS) plus lovastatin (sterol starvation) were 4- and 8-fold higher, respectively, than in LPDS plus 25-hydroxycholesterol (sterol feeding), resulting in 4-fold higher 3beta-hydroxysterol Delta(14)-reductase activity. No variations in LBR mRNA and protein levels were detected in the same conditions. The induction of TM7SF2 gene expression is turned-on by promoter activation in response to low cell sterol levels and is mediated by SREBP-2. The results suggest a primary role of C14SR in human cholesterol biosynthesis, whereas LBR role in the pathway remains unclear.
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PMID:Sterol dependent regulation of human TM7SF2 gene expression: role of the encoded 3beta-hydroxysterol Delta14-reductase in human cholesterol biosynthesis. 1678 88

The two-component alkanesulfonate monooxygenase system utilizes reduced flavin as a substrate to catalyze a unique desulfonation reaction during times of sulfur starvation. The importance of protein-protein interactions in the mechanism of flavin transfer was analyzed in these studies. The results from affinity chromatography and cross-linking experiments support the formation of a stable complex between the flavin mononucleotide (FMN) reductase (SsuE) and monooxygenase (SsuD). Interactions between the two proteins do not lead to overall conformational changes in protein structure, as indicated by the results from circular dichroism spectroscopy in the far-UV region. However, subtle changes in the flavin environment of FMN-bound SsuE that occur in the presence of SsuD were identified by circular dichroism spectroscopy in the visible region. These data are supported by the results from fluorescent spectroscopy experiments, where a dissociation constant of 0.0022 +/- 0.0010 muM was obtained for the binding of SsuE to SsuD. Based on these studies, the stoichiometry for protein-protein interactions is proposed to involve a 1:1 monomeric association of SsuE with SsuD.
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PMID:Detection of protein-protein interactions in the alkanesulfonate monooxygenase system from Escherichia coli. 1699 55

Synechococcus elongatus PCC 7942 was able to grow with several S sources. The sulphur metabolizing enzymes viz. ATP sulphurylase, cysteine synthase, thiosulphate reductase and L- and D-cysteine desulphydrases were regulated by sulphur sources, particularly by sulphur amino acids and organic sulphate esters. Sulphur starvation reduced ATP sulphurylase and cysteine synthase whereas reduced glutathione appreciated Cys degradation activity. With partially purified enzymes apparent Km values for sulphate, ATP, D- and L-Cys, thiosulphate, sulphide and O-acetyl serine were in a range of 12-50 microM. p-Nitrophenyl sulphate inhibited ATP sulphurylase competitively. Met was a feedback inhibitor of several key enzymes.
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PMID:Catalytic and regulatory properties of sulphur metabolizing enzymes in cyanobacterium Synechococcus elongatus PCC 7942. 1699 35

Cholesterol metabolism is particularly active in malignant, proliferative cells, whereas cholesterol starvation has been shown to inhibit cell proliferation. Inhibition of enzymes involved in cholesterol biosynthesis at steps before the formation of 7-dehydrocholesterol has been shown to selectively affect cell cycle progression from G(2) phase in human promyelocytic HL-60 cells. In the present work, we explored whether cholesterol starvation by culture in cholesterol-free medium and treatment with different distal cholesterol biosynthesis inhibitors induces differentiation of HL-60 cells. Treatment with SKF 104976, an inhibitor of lanosterol 14-alpha demethylase, or with zaragozic acid, which inhibits squalene synthase, caused morphologic changes alongside respiratory burst activity and expression of cluster of differentiation antigen 11c (CD11c) but not cluster of differentiation antigen 14. These effects were comparable to those produced by all-trans retinoic acid, which induces HL-60 cells to differentiate following a granulocyte lineage. In contrast, they differed from those produced by vitamin D(3), which promotes monocyte differentiation. The specificity of the response was confirmed by addition of cholesterol to the culture medium. Treatment with PD 98059, an inhibitor of extracellular signal-regulated kinase, abolished both the activation of NADPH oxidase and the expression of the CD11c marker. In sharp contrast, BM 15766, which inhibits sterol Delta(7)-reductase, failed to induce differentiation or arrest cell proliferation. These results show that changes in the sterol composition may trigger a differentiation response and highlight the potential of cholesterol pathway inhibition as a possible tool for use in cancer therapy.
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PMID:Cholesterol starvation induces differentiation of human leukemia HL-60 cells. 1740 48

Stalled replication forks produced by three different ways of depleting deoxynucleoside triphosphate showed different capacities to undergo "replication fork reversal." This reaction occurred at the stalled forks generated by hydroxyurea treatment, was impaired under thermal inactivation of ribonucleoside reductase, and did not take place under thymine starvation.
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PMID:Double-strand break generation under deoxyribonucleotide starvation in Escherichia coli. 1752 1

Soybean seeds are a major source of protein, but contain low levels of sulfur-containing amino acids. With the objective of studying the sulfur assimilation pathway of soybean, a full-length cDNA clone for 5'-adenylylsulfate reductase (APS reductase) was isolated and characterized. The cDNA clone contained an open reading frame of 1414 bp encoding a 52 kDa protein with a N-terminal chloroplast/plastid transit peptide. Southern blot analysis of genomic DNA indicated that the APS reductase in soybean is encoded by a small multigene family. Biochemical characterization of the heterologously expressed and purified protein shows that the clone encoded a functional APS reductase. Although expressed in tissues throughout the plant, these analyses established an abundant expression of the gene and activity of the encoded protein in the early developmental stages of soybean seed, which declined with seed maturity. Sulfur and phosphorus deprivation increased this expression level, while nitrogen starvation repressed APS reductase mRNA transcript and protein levels. Cold-treatment increased expression and the total activity of APS reductase in root tissues. This study provides insight into the sulfur assimilation pathway of this nutritionally important legume.
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PMID:The role of 5'-adenylylsulfate reductase in the sulfur assimilation pathway of soybean: molecular cloning, kinetic characterization, and gene expression. 1776 Dec 1

Among the 118 genes upregulated by Pseudomonas aeruginosa in response to iron starvation [Ochsner, U. A., Wilderman, P. J., Vasil, A. I., and Vasil, M. L. (2002) Mol. Microbiol. 45, 1277-1287], we focused on the products of the two genes encoding electron transfer proteins, as a means of identifying the redox partners of the heme oxygenase (pa-HO) expressed under low-iron stress conditions. Biochemical and spectroscopic investigations demonstrated that the bfd gene encodes a 73-amino acid protein (pa-Bfd) that incorporates a [2Fe-2S]2+/+ center, whereas the fpr gene encodes a 258-residue NADPH-dependent ferredoxin reductase (pa-FPR) that utilizes FAD as a cofactor. In vitro reconstitution of pa-HO catalytic activity with the newly characterized proteins led to the surprising observation that pa-FPR efficiently supports the catalytic cycle of pa-HO, without the need of a ferredoxin. In comparison, electron transfer from pa-Bfd to pa-HO is sluggish, which strongly argues against the possibility that the seven electrons needed by pa-HO to degrade biliverdin are transferred from NADPH to pa-HO in a ferredoxin (Bfd)-dependent manner. Given that pa-HO functions to release iron from exogenous heme acquired under iron-starvation conditions, the use of a flavoenzyme rather than an iron-sulfur center-containing protein to support heme degradation is an efficient use of resources in the cell. The crystal structure of pa-FPR (1.6 A resolution) showed that its fold is comparable that of the superfamily of ferredoxin reductases and most similar to the structure of Azotobacter vinelandii FPR and Escherichia coli flavodoxin reductase. The latter two enzymes interact with distinct redox partners, a ferredoxin and a flavodoxin, respectively. Hence, findings reported herein extend the range of redox partners recognized by the fold of pa-FPR to include a heme oxygenase (pa-HO).
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PMID:Biochemical and structural characterization of Pseudomonas aeruginosa Bfd and FPR: ferredoxin NADP+ reductase and not ferredoxin is the redox partner of heme oxygenase under iron-starvation conditions. 1791 50

Mycobacterium tuberculosis is a successful pathogen largely due to its ability to persist in humans while evading the host immune system. Rv2557 and Rv2558 are two uncharacterized proteins which have been found to be present in the human granuloma along with other important proteins like isocitrate lyase and nitric oxide reductase which are necessary for long-term persistence. The two proteins are up-regulated in in vitro carbon-starvation conditions designed to mimic the latent stage. Genes corresponding to Rv2557 and Rv2558 are found only in Mycobacterium sp. so far and share high sequence identity of 65.4% at the protein level. In the present study we have cloned and purified the proteins as part of a long-term goal to understand their functional roles and importance to the pathogen. We have probed for their biophysical properties. The proteins are monomeric and do not interact with each other as revealed by size-exclusion chromatography and pull-down assays. Circular dichroism experiments involving temperature and chemical denaturation studies demonstrate that Rv2557 is more structured compared to Rv2558, which is surprising, given the high sequence conservation between them. In fact the free energy change (DeltaG(0)) of Rv2557 during guanidium chloride induced denaturation is higher than Rv2558 indicating higher structural stability. The unfolding studies indicate that overall both proteins unfold in a cooperative two state process but adopt different modes of stabilization. The present work sets the stage for further experiments to probe the functions of the proteins.
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PMID:Cloning, purification and comparative structural analysis of two hypothetical proteins from Mycobacterium tuberculosis found in the human granuloma during persistence and highly up-regulated under carbon-starvation conditions. 1864 Feb 78


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