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

1. Optimum conditions were established for determining the activities of the NADP(+)-linked enzymes, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and isocitrate dehydrogenase, in mosquito tissues. 2. The activity of each dehydrogenase was determined in samples of mosquitoes of different ages throughout the life-span. The specific-activity curves attained maximal values in the pupal or early adult period. From these maxima an 81% decrease in glucose 6-phosphate-dehydrogenase and 67% decrease in 6-phosphogluconate-dehydrogenase activities occurred after the tenth day of adult life; a 77% decrease in isocitrate-dehydrogenase activity occurred before the fifth day. 3. The activity differences were found in different body regions as well as in whole organisms. 4. Starvation of the larva or adult did not result in decreases in enzyme activity. 5. These findings support the hypothesis that the activities of enzymes that form NADPH are related to the biosynthetic activity, for the enzyme activities increased during the period of cellular growth and decreased during the aging period.
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PMID:Nicotinamide-adenine dinucleotide phosphate enzymes in the mosquito during growth and aging. 438 47

1. The concentrations of the oxidized and reduced substrates of the ;malic' enzyme (EC 1.1.1.40) and isocitrate dehydrogenase (EC 1.1.1.42) were measured in freeze-clamped rat livers. By assuming that the reactants of these dehydrogenase systems are at equilibrium in the cytoplasm the [free NADP(+)]/[free NADPH] ratio was calculated. The justification of the assumption is discussed. 2. The values of this ratio obtained under different nutritional conditions (well-fed, 48hr.-starved, fed with a low-carbohydrate diet, fed with a high-sucrose diet) were all of the same order of magnitude although characteristic changes occurred on varying the diet. The value of the ratio fell on starvation and on feeding with the low-carbohydrate diet and rose slightly on feeding with the high-sucrose diet. 3. The mean values of the ratio were calculated to be between 0.001 and 0.015, which is about 100000 times lower than the values of the cytoplasmic [free NAD(+)]/[free NADH] ratio. 4. The differences in the redox state of the two nicotinamide-adenine dinucleotide couples can be explained on a simple physicochemical basis. The differences are the result of equilibria that are determined by the equilibrium constants of a number of highly active readily reversible dehydrogenases and transaminases and the concentrations of the substrates and products of these enzymes. 5. The decisive feature is the fact that the NAD and NADP couples share substrates. This sharing provides a link between the redox states of the two couples. 6. The application of the method of calculation to data published by Kraupp, Adler-Kastner, Niessner & Plank (1967), Goldberg, Passonneau & Lowry (1966) and Kauffman, Brown, Passonneau & Lowry (1968) shows that the redox states of the NAD and NADP couples in cardiac-muscle cytoplasm and in mouse-brain cytoplasm are of the same order as those in rat liver. 7. The determination of the equilibrium constant at 38 degrees , pH7.0 and I 0.25 (required for the calculation of the [free NADP(+)]/[free NADPH] ratio), gave a value of 3.44x10(-2)m for the ;malic' enzyme (with CO(2) rather than HCO(3) (-) as the reactant) and a value of 1.98x10(-2)m(-1) for glutathione reductase.
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PMID:The redox state of free nicotinamide-adenine dinucleotide phosphate in the cytoplasm of rat liver. 439 Oct 39

In order to study the quantitative relationship between fatty acid synthesis and pentose phosphate-cycle activity under different hormonal and dietary conditions affecting the extent of glucose uptake, cells isolated from rat epididymal adipose tissue were incubated in bicarbonate buffer containing [U-(14)C]-, [1-(14)C]- or [6-(14)C]-glucose. From the amount of glucose taken up, the production of lactate and pyruvate, and the incorporation of (14)C from differently labelled [(14)C]glucose into CO(2), fatty acids and glyceride glycerol, the rates of glucose metabolism via different pathways and the extent of lipogenesis under various experimental conditions were determined. The contribution of the pentose phosphate-cycle to glucose metabolism under normal conditions was calculated to be 8%. Starvation and re-feeding, and the presence of insulin, caused an enhancement of glucose uptake, pentose phosphate-cycle activity and fatty acid synthesis. Plots of both pentose phosphate-cycle activity and fatty acid synthesis versus glucose uptake revealed that the extent of glucose uptake, over a wide range, determines the rates of fatty acid synthesis and glucose metabolism via the pentose phosphate cycle. A balance of formation and production of nicotinamide nucleotides in the cytoplasm was established. The total amount of cytoplasmic NADH and NADPH formed was only in slight excess over the hydrogen equivalents required for the synthesis of fatty acids, glyceride glycerol and lactate. Except in cells from starved animals, the pentose phosphate cycle was found to provide only about 60% of the NADPH required for fatty acid synthesis. The results are discussed with respect to an overall control of the different metabolic and biosynthetic reactions in the fat-cells by the amount of glucose transported into the cell.
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PMID:Interrelationship and control of glucose metabolism and lipogenesis in isolated fat-cells. Effect of the amount of glucose uptake on the rates of the pentose phosphate cycle and of fatty acid synthesis. 440 62

1. The conversion of [U-(14)C]glucose into carbon dioxide, cholesterol and fatty acids in liver slices and the activities of ;malic' enzyme, citrate-cleavage enzyme, NADP-linked isocitrate dehydrogenase and hexose monophosphate-shunt dehydrogenases in the soluble fraction of homogenates of liver were measured in chicks that were starved or starved then fed. 2. In newly hatched chicks the incorporation of [U-(14)C]glucose and the activity of ;malic' enzyme did not increase unless the birds were fed. The response to feeding of [U-(14)C]glucose incorporation into fatty acids increased as the starved chicks grew older. 3. Citrate-cleavage enzyme activity increased slowly even when the newly hatched chicks were unfed. On feeding, citrate-cleavage enzyme activity increased at a much faster rate. 4. In normally fed 20-day-old chicks starvation decreased the incorporation of [U-(14)C]glucose into all three end products and depressed the activities of ;malic' enzyme and citrate-cleavage enzyme. Re-feeding increased all of these processes to normal or higher-than-normal levels. 5. In both newly hatched and 20-day-old chicks starvation increased the activity of isocitrate dehydrogenase and feeding or re-feeding decreased it. 6. Very little change in hexose monophosphate-shunt dehydrogenase activity was observed during the dietary manipulations. 7. The results indicate that increased substrate delivery to the liver is the principal stimulus to the increased rate of glucose metabolism observed in newly hatched chicks. The results also suggest that changes in the activities of ;malic' enzyme and citrate-cleavage enzyme are secondary to an increased flow of metabolites through the glucose-to-fatty acid pathway and that the dehydrogenases of the hexose monophosphate shunt play a minor role in NADPH production for fatty acid synthesis.
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PMID:The effect of starvation and starvation followed by feeding on enzyme activity and the metabolism of [U-14C]glucose in liver from growing chicks. 566 80

Addition of liver cytosol from 16 hr-starved rats treated with 6-aminonicotinamide to rat liver microsomes caused potentiation of the anti-carboxylesterase action of ethyl-p-nitrophenyl phenylphosphonothioate (EPN). This was not found when liver cytosol from non-pretreated rats after 16 hr-starvation was used. This potentiation of EPN-induced inhibition of carboxylesterase may be, at least in part, explained by the fact that treatment of rats with 6-aminonicotinamide resulted in a significant increase in NADPH level in liver cytosol which, in turn, stimulated formation of an EPN oxygen analog, a potent inhibitor of carboxylesterase, through cytochrome P-450-coupled monooxygenase.
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PMID:Potentiation of EPN-induced inhibition of liver microsomal carboxylesterase by addition of liver cytosol from 6-aminonicotinamide-treated, starved rats. 623 51

Mice were found to convert acetone to lactate at appreciable rates. The conversion of acetone to gluconeogenic precursors could provide additional glycolytic intermediates that would allow the more complete utilization of lipid stores and increase survival time during starvation. In mice that were starved for 3 days or were provided with acetone in the drinking water the acetone-metabolizing pathway was induced to levels severalfold normal. Mice heterozygous for obesity-producing mutations, either obese (ob/+) or diabetes (db/+), showed induction of the activity of this pathway to a significantly higher degree than did homozygous normal (+/+) mice of the same strain. This more effective conversion of acetone to lactate exhibited by heterozygous mice could account for their prolonged survival on a starvation regimen compared to that of normal homozygotes. The rate-limiting step in the pathway appears to be the conversion of acetone to a hydroxylated derivative. The enzyme system effecting this conversion is an NADPH-requiring microsomal oxygenase found in the liver.
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PMID:Acetone metabolism in mice: increased activity in mice heterozygous for obesity genes. 692 21

We have examined the interconversion of cortisone (E) and cortisol (F) in rat lung homogenate and microsomal fraction and in the isolated rat lung perfused with Krebs bicarbonate solution containing 4.5% albumin. In the perfused lung the apparent Km was 5.1 microM E and the Vmax was 9 nmol . g(-1) . min-1. The ability of the lung to reduce E to F was enhanced both by 7 days prior exposure of the rat to an ambient temperature of 2 degrees C and by starvation of the rat for 3 days. The activity was inhibited by adrenalectomy and castration of 7 days duration. Whereas little steroid oxidation occurred in the perfused lung, preparations of lung homogenates and microsomal fraction readily reduced or oxidised the 11-position of the corticoid molecule depending on the preponderance of either NADPH or NADP, respectively. We conclude, that the predominance of the reductive reaction in the whole rat lung under physiological conditions reflects the very active pentose-phosphate shunt in the lung, which produces NADPH. We suggest that this ability of the lung to activate E to F may exert a fine control over the arterial concentration of unbound, physiologically active, 11-hydroxylated steroid.
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PMID:The physiological significance of 11 beta-hydroxysteroid dehydrogenase in the rat lung. 695 69

We examined the relationship between glucose-induced insulin release and the intermediary metabolism of islets from fed and fasted rats. Isolated islets were perifused and insulin release measured in the effluent. At various times after switching islets from 2.4 to 8.6 or 14.5 mM glucose or from 2.4 to 14.5 and back to 2.4 mM glucose, islets were quickly frozen, freeze dried, and subsequently analyzed for tissue content of glucose-6-P, fructose-1,6-P2 plus triose-P, Pi, ATP, ADP, 5'-AMP, NADH, NADPH, total NAD, and total NADP using enzymatic fluorometric procedures. When islets from fed rats were exposed to high glucose, there were concomitant increases of insulin release and islet content of glucose-6-P, fructose-1,6-P2 plus triose-P, NADH, and NADPH. During stimulation Pi and 5'-AMP content fell markedly. The total adenine nucleotide content remained constant. Similar secretory and metabolic changes occurred when 1.5 mM Pi was added to the perifusion fluid. When glucose-stimulated islets were switched back to low glucose for 10 min, all substances but fructose-1,6-P2 plus triose-P, 5'-AMP, NADPH, and possibly ATP returned to the prestimulatory level. Starvation of rats for 3 days blocked the secretory response to 8.6 mM glucose. Fructose-1,6-P2 plus triose-P rose but it did not attain the level existing in islets from fed rats. The ratios (ATP)/(5'-AMP) and (ATP)/(Pi)(adp) increased to the values observed in glucose-stimulated islets of fed rats. The metabolic changes in islets from fed rats exposed to high glucose are consistent with an activation of glycolysis occurring concomitantly with stimulated rates of insulin release. This occurs despite the decrease of important activators of glycolysis--Pi and 5'-AMP. The enhanced glycolysis possibly results from P-fructokinase activation by increased fructose-6-P levels. Activation of glycolysis with 8.6 mM glucose was not as pronounced in islets from starved rats. Despite the different secretory response of islets from fet and fasted rats, the changes of phosphorylation state in the islets, in particular, Pi and 5'-AMP levels, were similar.
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PMID:Effects of glucose on insulin release and on intermediary metabolism of isolated perifused pancreatic islets from fed and fasted rats. 699 11

Two groups of weanling male Sprague-Dawley rats were fed a semisynthetic diet (ad libitum group) and 50% of that consumed by the ad libitum group (restricted group) for 49 days. Compared to the ad libitum group, the animals of the restricted group gained 55% less in body weight and had 60% smaller livers. While serum glucose, urea nitrogen, uric acid and lipids were lowered in the restricted animals, other serum biochemical parameters remained unchanged. The in vitro activities of hepatic drug-metabolizing enzymes were increased two- to threefold in the restricted animals. Feed restriction also caused a significant increase in the activities of NADPH-generating enzymes of liver and adipose tissue; however, the enzymes not concerned with the production of NADPH remained unaffected by feed restriction. It is concluded that feed restriction, unlike starvation, enhanced activities of drug-metabolizing enzymes as well as NADPH-generating enzymes.
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PMID:Alterations of NADPH-generating and drug-metabolizing enzymes by feed restriction in male rats. 714 12

A single catalase enzyme was produced by the anaerobic bacterium Bacteroides fragilis when cultures at late log phase were shifted to aerobic conditions. In anaerobic conditions, catalase activity was detected in stationary-phase cultures, indicating that not only oxygen exposure but also starvation may affect the production of this antioxidant enzyme. The purified enzyme showed a peroxidatic activity when pyrogallol was used as an electron donor. It is a hemoprotein containing one heme molecule per holomer and has an estimated molecular weight of 124,000 to 130,000. The catalase gene was cloned by screening a B. fragilis library for complementation of catalase activity in an Escherichia coli catalase mutant (katE katG) strain. The cloned gene, designated katB, encoded a catalase enzyme with electrophoretic mobility identical to that of the purified protein from the B. fragilis parental strain. The nucleotide sequence of katB revealed a 1,461-bp open reading frame for a protein with 486 amino acids and a predicted molecular weight of 55,905. This result was very close to the 60,000 Da determined by denaturing sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified catalase and indicates that the native enzyme is composed of two identical subunits. The N-terminal amino acid sequence of the purified catalase obtained by Edman degradation confirmed that it is a product of katB. The amino acid sequence of KatB showed high similarity to Haemophilus influenzae HktE (71.6% identity, 66% nucleotide identity), as well as to gram-positive bacterial and mammalian catalases. No similarities to bacterial catalase-peroxidase-type enzymes were found. The active-site residues, proximal and distal hemebinding ligands, and NADPH-binding residues of the bovine liver catalase-type enzyme were highly conserved in B. fragilis KatB.
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PMID:Biochemical and genetic analyses of a catalase from the anaerobic bacterium Bacteroides fragilis. 776 8


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