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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Formation of sedoheptulose-7-phosphate and ketopentose phosphate was studied in vitro as affected by epinephrine and cAMP. No effect of epinephrine on the activity of transketolase was found with ribose-5-phosphate as a substrate of the nonoxidative reactions of the pentose phosphate ccyle. Epinephrine and cAMP enhance the formation of ketopentoses and sedoheptulose with glycogen as a main carbohydrate source, which is most pronounced in the experiments with cold preincubation. The phosphorylase system mediate influence of epinephrine and cAMP on the nonoxidative reactions products may be assumed.
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PMID:[Adrenaline and cyclic AMP stimulation of ketopentose and sedoheptulose formation in rat liver homogenates]. 18 67

Forty-three independent variants of the Novikoff hepatoma cell line have been isolated for their ability to use D-xylose, D-ribose, and/or L-arabinose as a sole carbon and energy source. The variants exhibited marked morphological changes and a loss or decrease of cloning efficiency in soft agar. The xylose and arabinose variants showed similar phenotypes while the ribose variants were a phenotypically heterogenous group. Two major classes of variants were found with regard to their specificity for pentoses: one class could grow on ribose, xylose, or arabinose, while the second class grew only on ribose. The lack of specificity for pentose use was correlated with the ability to use pentitols for growth. The frequency of pentose-utilizing clones was 5 X 10(-2) to 10(-3), and nitrosoguanidine treatment increased this frequency tenfold. Fluctuation analyses showed the appearance of pentose-utilizing variants to be a random event. Of the variants examined, 84% expressed a stable pentose phenotype, and of those, 6% were cold sensitive and 8% were temperature sensitive for pentose utilization. In addition to the suggested mutational basis for the pentose phenotype, two variants showed a large increase in chromosome number from 73 +/- 3 to 132 +/- 10.
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PMID:Pentose-utilizing variants of Novikoff hepatoma cells: phenotypic characterization. 57 Mar 6

1. The response to thermal acclimation of five key rate-limiting enzymes of intermediary metabolism and of six degradative enzymes was measured in tissue extracts of adult Drosophila melanogaster which had been acclimated for 4 days to 15, 25 or 30 degrees C. 2. Three enzymes of intermediary metabolism (HK, alpha-GPDH and CO) showed positive thermal compensation, which is the type of response characteristic of the enzymes involved in energy metabolism in vertebrate ectotherms. 3. The data obtained for CS and G6PDH showed no evidence for increased activity of TCA cycle nor of the pentose phosphate pathway upon cold acclimation in D. melanogaster. 4. Two degradative enzymes, ADH and non-specific esterase, showed inverse thermal compensation which is the type of response characteristic of degradative enzymes in vertebrate ectotherms. 5. In contrast to the situation in vertebrate ectotherms, catalase and the three lysosomal enzymes assayed (APH, acid DNase and acid RNase) displayed positive rather than inverse compensation. 6. The results presented here extend the data on the range of D. melanogaster enzymes which show compensation upon thermal acclimation and on the type of acclimation response which occurs.
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PMID:The effect of acclimation temperature on enzyme activity in Drosophila melanogaster. 165 Dec 3

The effects of lowering the temperature from 25 degrees C to 2-8 degrees C on carbohydrate metabolism by plant cells are considered. Particular emphasis is placed on the mechanism of cold-induced sweetening in tubers of potato (Solanum tuberosum). Temperatures between 0 and 10 degrees C were shown to cause a marked reduction in the rate of respiration of a wide range of plant tissues. At these temperatures the ability of suspension cultures of soybean (Glycine max), and callus cultures and tubers of potato to metabolize [14C]glucose was appreciably diminished. The detailed distribution of 14C showed that lowering the temperature decreased the proportion of the metabolized [14C]glucose that entered the respiratory pathways and increased the proportion converted to sucrose. Pulse and chase experiments, in which [14C]glucose was supplied to potato tubers at 2 and 25 degrees C, showed that lowering the temperature led to accumulation of label in hexose 6-phosphates, which were subsequently converted to sucrose. The patterns of 14CO2 production from specifically labelled [14C]glucose supplied to soybean suspension cultures and disks of potato tuber suggested that lowering the temperature reduced the activity of glycolysis more than that of the oxidative pentose phosphate pathway. It is argued that the above experiments demonstrate that lowering the temperature not only reduces the rate of carbohydrate metabolism but also alters the relative activities of the different pathways involved. A disproportionate reduction in glycolysis at the lower temperatures is suggested. Mature tubers of many varieties of potato accumulate sucrose and hexose when stored between 2 and 10 degrees C. Starch is the source of carbon for this synthesis of sugar. We could not detect cytosolic fructose-1,6-bisphosphatase in potato tubers and suggest that carbon for sugar synthesis in the cold leaves the amyloplast, not as triose phosphate, but probably as a six-carbon compound. Evidence is presented that phosphofructokinase (EC 2.7.1.11) plays a major role in regulating the entry of hexose 6-phosphates into glycolysis in potato tubers. Phosphofructokinase was purified from potato tubers and shown to consist of four forms. Three of these forms were shown to have higher Q10 values over the range 2-6 degrees C than over the range 12-16 degrees C and are regarded as being cold-labile. No such cold-lability was detected for the key enzymes involved in sucrose synthesis and the oxidative pentose phosphate pathway.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of low temperature on the respiratory metabolism of carbohydrates by plants. 297 65

The relative contribution of carbohydrate and lipid energy metabolism in liver tissue of temperature-acclimated striped bass was examined in vitro. Respirometry experiments were conducted to assess the role of various endogenous foodstuffs in providing reduced two-carbon fragments for aerobic metabolism. Liver composition was measured as a reflection of foodstuff flux and storage. Catabolism of 14C-labeled substrates to 14CO2 was monitored to estimate the tissue capacity for utilization of various classes of compounds. When measured at the temperature of acclimation, oxygen uptake (VO2) by liver slices shows near perfect compensation between 15 and 25 degrees C, whereas a 2.75-fold increase is found between 5 and 15 degrees C. Respiratory quotients (R.Q.) near unity are found at 5 degrees C and decrease to 0.85 and 0.82 at 15 and 25 degrees C, respectively. Inhibition of VO2 by iodoacetic acid, a glycolytic inhibitor, is near 60% at 5 degrees C and decreases to 30-40% at 15 and 25 degrees C. Evolution of 14CO2 from 14C-labeled glucoses and palmitate confirms a conservation of liver tissue capacity for carbohydrate utilization between acclimation temperatures of 5 and 15 degrees C, and an increasing capacity for utilization of fatty acids as temperature increases. Ratios of 14CO2 from 14C-6-and 14C-1-labeled glucoses indicate a relative increase in the participation of the pentose shunt in carbohydrate metabolism with cold acclimation. The results are consistent with an increasing reliance on carbohydrates for energy metabolism in the cold, whereas lipid substrates are utilized more at warm temperatures. These changes may be adaptive in partitioning energy reserves for seasonal activities of migration and reproduction.
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PMID:Metabolic responses of striped bass (Morone saxatilis) to temperature acclimation. I. Alterations in carbon sources for hepatic energy metabolism. 733 22

In order to examine glucose metabolism in liver grafts during cold preservation (24 and 48 hr), warm ischemia (60 and 120 min), a combination of the two and reperfusion, the amount of protein and mRNA of glucose transporter 2 and the activities of enzymes in glycolysis (glucokinase, phosphofructokinase, pyruvatekinase), gluconeogenesis (glucose 6-phosphatase, fructose 1,6-bisphosphatase), and the pentose phosphate pathway (glucose 6-phosphate dehydrogenase) were measured. It appeared that glucose transport, the pentose phosphate pathway, and gluconeogenesis were maintained during cold preservation and warm ischemia. The activity of glucokinase significantly decreased from the control value of 1.33 +/- 0.23 IU/g protein to 0.70 +/- 0.17 (24 hr, P<0.05) and 0.57 +/- 0.12 (48 hr, P<0.01) only during cold preservation. However, the activity of phosphofructokinase significantly decreased from the control value of 4.37 +/- 0.06 IU/g protein to 2.67 +/- 0.15 (60 min, P<0.0001) and 1.53 +/- 0.06 (120 min, P<0.0001) only during warm ischemia. This indicates that glycolysis deteriorates during both cold preservation and warm ischemia and demonstrates further that the balance between glycolysis and gluconeogenesis shifts to gluconeogenesis. Even when cold preservation was combined with warm ischemia, the activity of glucokinase decreased only during cold preservation and the activity of phosphofructokinase decreased only during warm ischemia. Furthermore, these changes were time-dependent. It is suggested that they can be used as a clock to measure the durations of cold preservation and warm ischemia separately and that the magnitude of an ischemic injury to a liver and a liver graft's viability can be indirectly estimated before transplantation.
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PMID:Changes in glucose transporter 2 and carbohydrate-metabolizing enzymes in the liver during cold preservation and warm ischemia. 862 51

Fatty acid synthesis from Na [1-14C] acetate in leucoplasts isolated from developing seeds of Brassica campestris was completely dependent on exogenous supply of ATP. None of the intermediates of glycolysis or pentose phosphate pathway tested could replace ATP in the reaction mixture. In absence of exogenously supplied ATP, maximum activity was obtained with glu-6-P (68%) followed by fru-6-P (50%) and PEP (44%), respectively. With other intermediates as energy sources, the activity ranged from 1 to 38%. In complementary experiments (presence of ATP), none of the metabolites gave activity higher than the ATP control activity. Under optimum conditions for fatty acid synthesis from acetate, Brassica leucoplasts readily utilized labelled glucose as the substrate for fatty acid synthesis. Omission of NADH and NADPH individually from the reaction mixtures containing labelled glucose resulted only in 46 and 20% loss in activity, respectively, compared to the corresponding losses of 56 and 50%, when labelled acetate was used as the substrate. Similarly, deletion of ATP from the reaction mixture containing glucose as the substrate decreased the rate of fatty acid synthesis by about 65%, while the corresponding decrease with acetate as the substrate was 96%. Inclusion of 5 mM cold acetate, pyruvate, malate and glu-6-P in the reaction mixture containing glucose as the labelled substrate reduced label incorporation into fatty acids by 38 to 69%, maximum reduction being observed with pyruvate followed by glu-6-P, acetate and malate, respectively. With labelled acetate as the substrate, maximum reduction in label incorporation was obtained with cold glucose (5 mM) followed by glu-6-P, pyruvate and malate, respectively. The study demonstrated the operation of complete glycolytic pathway in Brassica leucoplasts, allowing the plastids to use glucose as a source of carbon, reducing power and energy for fatty acid synthesis.
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PMID:Fatty acid synthesis by isolated leucoplasts from developing Brassica seeds: role of glycolytic intermediates as the source of carbon and energy. 921 33

We measured enzyme activities along a heterothermic tissue, the visceral retia mirabilia of the bluefin tuna, to test current theories of enzyme temperature adaptation. The heterothermic tissue model is ideal for the study of fundamental temperature adaptation because it eliminates confounding effects of whole animal acclimation. Enzymes were measured at six positions along the rete at four temperatures (15, 20, 25, and 30 degrees C). Five enzymes (aspartate aminotransferase, citrate synthase, glucose-6-phosphate dehydrogenase, glutamate dehydrogenase, and pyruvate kinase) exhibited a significant positive compensatory effect, with activity at the cold end of the rete 1.2-3.1 times higher than at the warm end. Two enzymes (alanine aminotransferase and lactate dehydrogenase) exhibited no significant compensation. On the basis of activation energies of enzymes along the rete, differences in activity were due to differences in enzyme concentration and not isozymes or enzyme modification. Analysis of the compensatory responses of the enzymes in light of their thermal sensitivities leads us to conclude that the pentose phosphate shunt is especially enhanced at the cold end of the rete.
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PMID:Enzyme adaptation along a heterothermic tissue: the visceral retia mirabilia of the bluefin tuna. 922 97

(31)P NMR spectroscopy offers a possibility to obtain a survey of all low-molecular-weight phosphorylated compounds in yeast. The yeast cells have been extracted using chloroform into a neutral aqueous phase. The use of high fields and the neutral pH extracts, which are suitable for NMR analysis, results in well-resolved (31)P NMR spectra. Two-dimensional NMR experiments, such as proton-detected heteronuclear single quantum ((1)H-(31)P HSQC) and (31)P correlation spectroscopy ((31)P COSY), have been used to assign the resonances. In the phosphomonoester region many of the signals could be assigned to known metabolites in the glycolytic and pentose phosphate pathways, although some signals remain unidentified. Accumulation of ribulose 5-phosphate, xylulose 5-phosphate, and ribose 5-phosphate was observed in a strain lacking transketolase activity when grown in synthetic complete medium. No such accumulation occurred when the cells were grown in yeast-peptone-dextrose medium. Trimetaphosphate (intracellular concentration about 0.2 mM) was detected in both cold methanol-chloroform and perchloric acid extracts.
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PMID:Identification and quantitation of phosphorus metabolites in yeast neutral pH extracts by nuclear magnetic resonance spectroscopy. 1040 95

Cold stress resulted in a decrease in the poly-beta-hydroxybutyrate (PHB) content of non-cold-acclimated Rhizobium DDSS69 cultures. Analysis of the specific activity of beta-ketothiolase and beta-hydroxybutyrate dehydrogenase revealed that decrease in PHB levels was a result of the inhibition of synthesis of PHB rather than an increase in its breakdown. Rhizobium ATR1, a cold-acclimated strain, revealed the presence of a stable PHB metabolism that did not show any significant differences either in PHB levels or in the activity of enzymes of the PHB metabolism under cold stress, suggesting that PHB is not involved in cold tolerance. Analysis of specific activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase of the pentose phosphate pathway showed the upward regulation of alternate pathways of carbohydrate metabolism under cold stress to rapidly generate energy to overcome the stress. There is diversity in the switching mechanisms of carbon metabolism among cold-acclimated and non-cold-acclimated Rhizobium isolates. Upward regulation of malate dehydrogenase in both isolates suggests that it is a critical input for cold tolerance.
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PMID:Poly-beta-hydroxybutyrate metabolism is affected by changes in respiratory enzymatic activities due to cold stress in two psychrotrophic strains of Rhizobium. 1111 98


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