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

The composition of the acid soluble nucleotide pool of Carp liver was determined by column chromatography, and its changes were followed during prolonged total fast. Total prolonged starvation caused substantial changes in the distribution of hepatocyte free nucleotides. Eleven months of starvation caused a reduction in the concentration of di- and triphosphate nucleosides as well as a diminution of the oxido-reduction of the hepatocyte. Only pyrimidine nucleoside monophosphates remained at concentration approaching those found in regularly fed Carp.
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PMID:[Effect of total and prolonged starvation on the acid soluble nucleotides in carp liver]. 2 15

Out of different azapyrimidines tested for their ability to affect metabolism of orotic acid in the liver of rats kept on food only 5-azacytidine resulted in the enhanced incorporation of orotate into liver RNA following 24 hr pretreatment. Similar effect was observed also in cycloheximide-treated animals. No stimulation of orotic acid utilization following 5-azacytidine or cycloheximidine treatment was observed in the liver of starved animals. Both drugs (but not other pyrimidine analogues tested) depressed markedly gastric secretion in rats and caused decreased evacuation of the stomach. The decreased secretion of pepsin and lower gastric acidity resulting in drug-simulated starvation of the treated animals are discussed in relation to the enhanced uptake of orotic acid into liver RNA.
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PMID:Lower gastric secretion and higher incorporation of orotic acid into liver RNA in rats treated with 5-azacytidine and cycloheximide. 7 86

Aspartate transcarbamylase is synthesized during exponential growth of Bacillus subtilis and is inactivated when the cells enter the stationary phase. This work is a study of the regulation of aspartate transcarbamylase synthesis during growth and the stationary phase. Using specific immunoprecipitation of aspartate transcarbamylase from extracts of cells pulse-labeled with tritiated leucine, we showed that the synthesis of the enzyme decreased very rapidly at the end of exponential growth and was barely detectable during inactivation of the enzyme. Synthesis of most cell proteins continued during this time. When the cells ceased growing because of pyrimidine starvation of a uracil auxotroph, however, synthesis and inactivation occurred simultaneously. Measurement of pools of pyrimidine nucleotides and guanosine tetra- and pentaphosphate demonstrated that failure to synthesize aspartate transcarbamylase in the stationary phase was not explained by simple repression by these compounds. The cessation of aspartate transcarbamylase synthesis may reflect the shutting off of a "vegetative gene" as part of the program of differential gene expression during sporulation. However, aspartate transcarbamylase synthesis decreased normally at the end of exponential growth at the nonpermissive temperature in a mutant strain that is temperature-sensitive in sporulation and RNA polymerase function. Cessation of aspartate transcarbamylase synthesis appeared to be normal in three other temperature-sensitive RNA polymerase mutants and in several classes of spo0 mutants.
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PMID:Aspartate transcarbamylase synthesis ceases prior to inactivation of the enzyme in Bacillus subtilis. 9 40

Urinary orotidine and orotic acid have been determined in a patient with purine nucleoside phosphorylase (PNP) deficiency under various dietary therapeutic conditions. For this purpose a new procedure for the analysis of both compounds has been developed, consisting of prefractionation with Dowex 1X8, followed by two HPLC steps on a micro Bondapak NH2 and a micro Bondapak C18 column. With this method normal as well as slightly elevated excretions of orotic acid have been found in our patient. No evidence was obtained for inhibition of OPRT by purine (deoxy)nucleosides as a cause of pyrimidine starvation. A significant increase of urinary orotidine was found after loading with allopurinol. For comparison excretory values in a patient with ornithine transcarbamylase deficiency and also in a patient with orotic aciduria type I are shown. The possible cause of the slight increase in urinary orotic acid in our patient has been discussed.
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PMID:Urinary excretion of orotic acid, orotidine and other pyrimidines in a patient with purine nucleoside phosphorylase deficiency. 10 38

Pre-irradiation starvation of exponentially growing Escherichia coli B/r Hcr+ thy-try- strain for thymine and tryptophan causes inhibition of pyrimidine dimer excision from ultraviolet damaged cells DNA. This inhibition of excision repair has not resulted in increasing ultraviolet sensitivity nor in increasing frequency of ultraviolet induced tryptophan revertants. The possible mechanisms of the non-excision repair in the prestarved cells, which is at least as accurate and effective as the whole dark repair in exponentially growing cells, are discussed.
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PMID:Inhibition of excision repair without influence upon UV-sensitivity and UV-mutability in Escherichia coli B/r Hcr+. 12 83

Repression of biosynthetic enzyme synthesis in Pseudomonas putida is incomplete even when the bacteria are growing in a nutritionally complex environment. The synthesis of four of the enzymes of the arginine biosynthetic pathway (N-acetyl-alpha-glutamokinase/N-acetylglutamate-gamma-semialdehyde dehydrogenase, ornithine carbamoyltransferase and acetylornithine-delta-transaminase) could be repressed and derepressed, but the maximum difference observed between repressed and derepressed levels for any enzyme of the pathway was only 5-fold (for ornithine carbamoyltransferase). No repression of five enzymes of the pyrimidine biosynthetic pathway (aspartate carbamoyltransferase, dihydro-orotase, dihydro-orotate dehydrogenase, orotidine-5'-phosphate pyrophosphorylase and orotidine-5'-phosphate decarboxylase) could be detected on addition of pyrimidines to minimal asparagine cultures of P. putida A90, but a 1-5- to 2-fold degree of derepression was found following pyrimidine starvation of pyrimidine auxotrophic mutants of P. putida A90. Aspartate carbamoyltransferase in crude extracts of P. putida A90 was inhibited in vitro by (in order of efficiency) pyrophosphate, CTP, UTP and ATP, at limiting but not at saturating concentrations of carbamoyl phosphate.
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PMID:Regulation of arginine and pyrimidine biosynthesis in Pseudomonas putida. 17 12

The absence of erythrocytic adenosine deaminase (ADA) or purine nucleoside phosphorylase (PNP) has been associated with severe immunodeficiency disease in children. We have developed a cell culture model to study the possible relationships between purine salvage enzymes and immunologic function using an established T cell lymphosarcoma (S49) and a potent inhibitor of ADA, erythro-9(2-hydroxy-3-nonyl) adenine (EHNA). Wild-type S49 cells are killed by dexamethasone or dbc AMP, and adenosine (5 muM) in the presence of an ADA inhibitor (6 muM EHNA) also prevents the growth of and kills these S49 cells. It has been proposed that adenosine is toxic to lymphoid cells by virtue of its ability to increase the intracellular concentrations of cyclic AMP. We examined the sensitivity of three mutants of S49 cells, with distinctive defects in some component of cyclic AMP metabolism or action, to killing by adenosine and EHNA. All three mutants are resistant to killing by isoproterenol or cholera toxin and two are resistant to dbc AMP itself, but all are sensitive to killing by adenosine and EHNA. Similarly, two dexamethasone-resistant S49 mutants are as sensitive to adenosine and EHNA as are the wildtype cells. We have also simulated the purine nucleoside phosphorylase deficiency in S49 cells by adding inosine and adenosine to the growth medium. In the presence of EHNA or inosine, the toxic effects of adenosine can be partially reversed by addition of (10-20 muM) uridine, an observation suggesting that adenosine is toxic as the result of its inducing pyrimidine starvation.
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PMID:Characterization of a cell culture model for the study of adenosine deaminase- and purine nucleoside phosphorylase-deficient immunologic disease. 18 61

The phenotype of certain mutations in pyrA, the gene encoding carbamylphosphate synthetase (CPSase), is expressed only in the presence od exogenous arginine. In unsupplemented media, synthesis of carbamylphosphate and growth was almost normal; in arginine-containing media, synthesis of carbamylphosphate stopped, as did growth, as a consequence of starvation for pyrimidine. Genetic and biochemical evidence suggests that arginine exerts this inhibition by repressing the synthesis of ornithine carbamyltransferase (OTCase), the intracellular presence of which is required for assembly of the unequal subunits and proper functioning of the mutant CPSase. After the addition of arginine to a culture of the mutant, CPSase activity (glutamine dependent) characteristic of the intact holoenzyme progressively decreased, whereas activity (ammonia dependent) characteristic of the free large (alpha) subunit increased. Extracts of mutant cells contain free small (beta) subunits, as demonstrated directly by in vitro complementation using purified alpha subunits from wild type. The mutant enzyme from cultures grown in the presence of arginine had a markedly decreased affinity for adenosine 5'-triphosphate. Mutations in argR that cause depressed synthesis of OTCase suppressed the phenotype, and a certain mutation in argI, the gene encoding OTCase, enhanced it. In vitro experiments using purified enzyme confirm the stimulatory effect of OTCase on the activity of mutant CPSase.
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PMID:Arginine-sensitive phenotype of mutations in pyrA of Salmonella typhimurium: role of ornithine carbamyltransferase in the assembly of mutant carbamylphosphate synthetase. 18 93

Sublines with single or multiple defects in purine "salvage" enzymes were isolated from the Chinese hamster fibroblastic line GMA32 through single or successive one-step selections for resistance to purine analogs. They were examined for their ability to incorporate purine bases and nucleosides into macromolecules, for their sensitivity to growth inhibitory purines, and for their rescue by exogenous purines from deprivation imposed by metabolic inhibitors of endogenous synthesis. The results show that a deficiency of either adenosine kinase (EC 2.7.1.20), adenine phosphoribosyltransferase (EC 2.4.2.7) or hypoxanthine guanine phosphoribosyltransferase (EC 2.4.2.8) abolishes the ability of adenine to cause cell death by interfering with pyrimidine synthesis; on the other hand, the pyrimidine starvation caused by adenosine is fully prevented only by a deficiency of adenosine kinase.
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PMID:The control of cell proliferation by preformed purines: a genetic study. I. Isolation and preliminary characterization of Chinese hamster lines with single or multiple defects in purine "salvage" pathways. 19 54

The human lymphoblast line WI-L2 is subject to growth inhibition by a combination of the adenosine deaminase (ADA; adenosine aminohydrolase, EC 3.5.4.4.) inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and adenosine. Although adenosine-induced pyrimidine starvation appears to contribute to this effect, uridine only partially reverses adenosine toxicity in WI-L2 and not at all in strain 107, an adenosine kinase-(ATP:adenosine 5'-phosphotransferase, EC 2.7.1.20) deficient derivative of WI-L2. Treatment of both cell lines with EHNA and adenosine leads to striking elevations in intracellular S-adenosyl-L-homocysteine (AdoHcy), a potent inhibitor of S-adenosyl-L-methionine (AdoMet)-dependent methylation reactions. The methylation in vivo of both DNA and RNA is inhibited by concentrations of EHNA and adenosine that elevate intracellular AdoHcy. Addition of 100 muM L-homocysteine thiolactone to cells treated with EHNA and adenosine enhances adenosine toxicity and further elevates AdoHcy to levels approximately 60-fold higher than those obtained in the absence of this amino acid, presumably by combining with adenosine to form AdoHcy in a reaction catalyzed by S-adenosylhomocysteine hydrolase (EC 3.3.1.1). In the adenosine kinase-deficient strain 107, a combination of ADA inhibition and L-homocysteine thiolactone markedly increases intracellular AdoHcy and inhibits growth even in the absence of exogenous adenosine. These results demonstrate a form of toxicity from endogenously produced adenosine and support the view that AdoHcy, by inhibiting methylation, is a mediator of uridine-resistant adenosine toxicity in these human lymphoblast lines. Furthermore, they suggest that AdoHcy may play a role in the pathogenesis of the severe combined immunodeficiency disease found in most children with heritable ADA deficiency.
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PMID:S-adenosylhomocysteine toxicity in normal and adenosine kinase-deficient lymphoblasts of human origin. 22 26


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