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At least 1,261 records · Page 70Linked to original sources
PubMed1968

Early effects of phytohaemagglutinin on glucose metabolism of normal human lymphocytes.

1. Phytohaemagglutinin induced early changes in the catabolism of glucose by normal human lymphocytes suspended in a bicarbonate buffer. During 4hr. incubation glucose utilization was almost doubled. 2. The rates of several reactions in the metabolism of glucose were estimated. Total pyruvate formation, lactate production and fatty acid synthesis were stimulated to the same degree as was glucose utilization. The pentose cycle and the glycogen synthesis were also stimulated but less than was glucose utilization. The pentose cycle was found to account for 1.4% and 0.9% of the total glucose utilization without and with phytohaemagglutinin respectively. In these cells rates of triose phosphate iso-merization were at least six to seven times the rate of glucose phosphorylation. On an average 55-60% of the total carbon dioxide evolved was derived from decarboxylation of pyruvate, 25-30% from the tricarboxylic acid cycle and about 15% from the pentose cycle. Observed ratios of (14)C specific yields in glycogen from [1-(14)C]- and [6-(14)C]-glucose could possibly be explained by assuming the existence of two separate glucose 6-phosphate pools. 3. During 4hr. incubation in bicarbonate buffer (14)C from [U-(14)C]serine was incorporated into perchloric acid-insoluble material. This incorporation was stimulated by phytohaemagglutinin but was almost completely inhibited by puromycin. Puromycin also abolished phytohaemagglutinin-induced stimulation of glycolysis.

Carbon Isotopes↗
PubMed1998

Carbon-flux distribution in the central metabolic pathways of Corynebacterium glutamicum during growth on fructose.

Growth of Corynebacterium glutamicum on fructose was significantly less than that obtained on glucose, despite similar rates of substrate uptake. This was in part due to the production of overflow metabolites (dihydroxyacetone and lactate) but also to the increased production of CO2 during growth on fructose. These differences in carbon-metabolite accumulation are indicative of a different pattern of carbon-flux distribution through the central metabolic pathways. Growth on glucose has been previously shown to involve a high flux (> 50% of total glucose consumption) via the pentose pathway to generate anabolic reducing equivalents. NMR analysis of carbon-isotope distribution patterns of the glutamate pool after growth on 1-13C- or 6-13C-enriched fructose indicates that the contribution of the pentose pathway is significantly diminished during exponential growth on fructose with glycolysis being the predominant pathway (80% of total fructose consumption). The increased flux through glycolysis during growth on fructose is associated with an increased NADH/NAD+ ratio susceptible to inhibit both glyceraldehyde-3-phosphate dehydrogenase and pyruvate dehydrogenase, and provoking the overflow of metabolites derived from the substrates of these two enzymes. The biomass yield observed experimentally is higher than can be estimated from the apparent quantity of NADPH associated with the pentose pathway and the flux through isocitrate dehydrogenase, suggesting an additional reaction yielding NADPH. This may involve a modified tricarboxylic acid cycle involving malic enzyme, expressed to significantly higher levels during growth on fructose than on glucose, and a pyruvate carboxylating anaplerotic enzyme.

Biological Transport↗
PubMed2001

The enhancement of glucose uptake caused by the collapse of gap junction communication is due to an increase in astrocyte proliferation.

We have previously shown that several gap junction uncouplers increase the uptake of glucose in astrocytes. The aim of the present work was to study whether the increase in glucose uptake was a consequence of the inhibition of gap junction communication and the purpose of this effect. Our results show that alpha-glycyrrhetinic acid and endothelin-1 increase the uptake of glucose in highly, but not in poorly, coupled astrocytes. This effect depended on connexin 43 levels and was abolished when the inhibition of gap junction communication was prevented by tolbutamide or ouabain. The inhibition of gap junctions increased the rate of glucose incorporation into DNA and RNA, which was inhibited by treatment with dehydroepiandrosterone, an inhibitor of glucose-6-phosphate dehydrogenase, the regulatory enzyme of the pentose phosphate pathway. The inhibition of gap junctions significantly increased astrocyte proliferation, which was counteracted by tolbutamide. These effects were not observed in poorly coupled astrocytes expressing low levels of connexin 43. The increase in astrocyte proliferation caused by gap junction inhibition was prevented when either glucose uptake or the pentose phosphate pathway were inhibited. We conclude that the inhibition of gap junction communication induces astrocyte proliferation, resulting in an enhancement of glucose uptake and its utilization through the pentose phosphate pathway to provide ribose-5-phosphate for the synthesis of nucleic acids.

Administration, Topical↗
PubMed1981

Evidence for biochemical and physiological differences between enzyme genotypes in Drosophila melanogaster.

The in vivo flux of carbon through the pentose shunt is investigated as a function of different 6-phosphogluconate dehydrogenase (6Pgd) and glucose-6-phosphate dehydrogenase (G6pd) genotypes by using differential radioactive labeling of the C-1 and C-6 positions of glucose. Alternative 6Pgd-G6pd genotypes are shown to differ in relative in vivo carbon flux through the pentose shunt. The relative in vitro specific activity differences between the 6PgdSS and 6PgdFF genotypes appear to be primarily responsible for these differences. In addition, the pentose-shunt activity is correlated with the rate of lipid synthesis. This correlation is consistent with the major metabolic function of the pathway, which is to produce NADPH for lipid synthesis. Taken together, the results of these experiments show that different genotypes of 6Pgd are associated with measurable biochemical and physiological differences. Higher order phenotypic differences of this kind must be demonstrated to support the hypothesis that natural selection can discriminate among allozymes of a given genetic locus.

Animals↗
PubMed2001

Frog oocytes: a living test tube for studies on metabolic regulation.

This review is intended to illustrate how live frog oocytes may be advantageously used to address the study of some problems of in vivo glucose metabolism. Glucose microinjected into the cells is preferentially committed to glycogen synthesis. We present evidence showing that both the direct and indirect pathways for polysaccharide deposition are operative in oocytes. A small amount of the injected glucose (<5%) is released as labeled CO2 mainly through the pentose-P pathway. Coinjection of NADP+ and glucose significantly stimulates 14CO2 production, half-maximal stimulation being obtained at 0.13 mM. Finally, we show the use of frog oocytes to measure in vivo the control coefficient of hexokinase on glycogen synthesis and the pentose-P pathway. A value of 0.7 was found for the control coefficient of hexokinase on glycogen synthesis, while the enzyme has no control at all over the pentose-P pathway. Therefore, the frog oocyte may be used as a living test tube for the study of almost any metabolic process of interest.

Animals↗
PubMed2002

Ultraviolet light-induced changes in the glucose-6-phosphate dehydrogenase activity of porcine corneas.

PURPOSE: Corneas have the high activity of the pentose phosphate pathway. To clarify the relevance of the pentose phosphate pathway to their antioxidant defense, we examined the activity of glucose-6-phosphate dehydrogenase (G6PDH), the rate-determining enzyme of the pathway, in corneas exposed to ultraviolet light (UV). METHODS: Fresh porcine eye globes were exposed to ultraviolet light A (UVA) or ultraviolet light C (UVC), and the tear film-removed eye globes to UVA. After UV exposure, the corneas were dissected from the eye globes and extracted with a saline solution, and the G6PDH activity in the extract was assayed. The G6PDH activity of unilateral opaque corneas, their paired, transparent corneas, and normal corneas, all of which were obtained from fresh, UV-unexposed eye globes, and the L-lactate dehydrogenase (LDH) activity of these opaque and normal corneas also were assayed. RESULTS: The G6PDH activity of corneas increased with UVA exposure, and decreased with long-term UVC exposure, although it increased with short-term UVC exposure. A UV-blocking contact lens screened corneas from the UVA-induced increase. Removal of the tear film enhanced the UVC-induced decrease. The G6PDH activity of unilateral opaque corneas was lower than that of paired, transparent corneas or normal corneas, all of which were obtained from fresh, UV-unexposed eye globes. The LDH activity of the opaque corneas was much higher than that of the normal corneas. CONCLUSION: Exposure of corneas to UVA or a small dose of UVC enhances the G6PDH activity, i.e., the pentose phosphate pathway. This activity enhancement may play an important role in corneal antioxidant defense against UV-induced oxidative stress. However, exposure of corneas to large doses of UVC appears to damage the pathway.

Animals↗
PubMed1987

Influence of cumene hydroperoxide and 4-hydroxynonenal on the glutathione metabolism during in vitro ageing of human skin fibroblasts.

Cumene hydroperoxide (Chp) and 4-hydroxynonenal (HNE) were used to investigate the effect of peroxidative challenge upon the glutathione (GSH) metabolism of human skin fibroblasts. Cellular GSH contents decreased during short-term incubations with Chp and oxidised glutathione (GSSG) was formed concomitantly. During longer incubations the GSH level was restored and the substrate flux through the pentose phosphate shunt increased. So in the presence of hydroperoxides the GSH level is maintained by reduction of GSSG. HNE caused a strong decrease in cellular GSH contents. Prolonged incubation with HNE lead to a rise in GSH contents above the basal level. The flux through the pentose phosphate shunt did not change during exposure to HNE. Hence, during incubation with HNE the cell maintains its GSH content by de novo synthesis of GSH. This conclusion is further substantiated by the findings with a cell strain deficient in GSH synthetase. These cells survived if incubated with Chp but not if exposed to HNE. GSH contents of normal cells from phase II (young) cultures and from phase III (aged) cultures responded similarly to Chp during short-term incubations and during a week of culture with the test compound. The flux through the pentose phosphate shunt rose much more in phase III than in phase II cells when incubated with the same concentration series of Chp. We conclude that during in vitro ageing the amount of NADPH needed to maintain cellular GSH levels in the presence of hydroperoxides increases, while the capacity to respond to such a challenge is not affected.

Adult↗
PubMed1970

Amino sugar sensitivity in Escherichia coli mutants unable to grow on N-acetylglucosamine.

Studies were conducted on two mutants of Escherichia coli that lack either glucosamine-6-phosphate deaminase or N-acetylglucosamine-6-phosphate deacetylase and which accumulate glucosamine-6-phosphate or N-acetylglucosamine-6-phosphate, respectively, when grown in the presence of N-acetylglucosamine. The addition of 10(-4) to 10(-5)mN-acetylglucosamine to these mutant strains caused a rapid and complete inhibition of growth on substrates that enter the catabolic pathways at or below the level of fructose-6-phosphate. Growth on glucose was inhibited to a lesser degree, whereas only minor inhibition occurred when the pentoses were used as substrates. Growth on gluconate was found to be totally unaffected by these levels of N-acetylglucosamine. The objective of this investigation was to determine the nature of this "amino sugar sensitivity" phenomenon and the conditions under which it could be overcome. It was found that this amino sugar sensitivity was abolished when an exogenous source of pentose such as uridine was included in the culture medium. Experiments are described indicating that the accumulated amino sugar phosphate metabolites interfere with an early step in hexose metabolism of both mutants, resulting in a pentose deficiency and consequent inhibition of growth on certain substrates.

Amidohydrolases↗
PubMed1994

Pathway of glycogen metabolism in Methanococcus maripaludis.

Methanococcus maripaludis, a facultatively autotrophic archaebacterium that grows with H2 or formate as the electron donor, does not assimilate sugars and other complex organic substrates. However, glycogen is biosynthesized intracellularly and commonly reaches values of 0.34% of the cellular dry weight in the early stationary phase. To determine the pathway of glycogen catabolism, specific enzymes of sugar metabolism were assayed in cell extracts. The following enzymes were found (specific activity in milliunits per milligram of protein): glycogen phosphorylase, 4.4; phosphoglucomutase, 10; glucose-6-phosphate isomerase, 9; 6-phosphofructokinase, 5.6, fructose-1,6-bisphosphatase, 10; fructose-1,6-bisphosphate aldolase, 4.2; triosephosphate isomerase, 44; glyceraldehyde-3-phosphate dehydrogenase, 26; phosphoglycerate kinase, 20; phosphoglycerate mutase, 78; enolase, 107; and pyruvate kinase, 4.0. Glyceraldehyde-3-phosphate dehydrogenase was NADP+ dependent, and the pyruvate kinase required MnCl2. The 6-phosphofructokinase had an unusually low pH optimum of 6.0. Four nonoxidative pentose-biosynthetic enzymes were found (specific activity in milliunits per milligram of protein): transketolase, 12; transaldolase, 24; ribulose-5-phosphate-3-epimerase, 55; and ribulose-5-phosphate isomerase, 100. However, the key enzymes of the oxidative pentose phosphate pathway, the reductive pentose phosphate pathway, and the classical and modified Entner-Duodoroff pathways were not detected. Thus, glycogen appears to be catabolized by the Embden-Meyerhoff-Parnas pathway. This result is in striking contrast to the nonmethanogenic archaebacteria that have been examined, among which the Entner-Doudoroff pathway is common. A dithiothreitol-specific NADP(+)-reducing activity was also found (8.5 mU/mg of protein). Other thiol compounds, such as cysteine hydrochloride, reduced glutathione, and 2-mercaptoethanesulfonic acid, did not replace dithiothreitol for this activity. The physiological significance of this activity is not known.

Dithiothreitol↗
PubMed1995

Genetic evidence of a major role for glucose-6-phosphate dehydrogenase in nitrogen fixation and dark growth of the cyanobacterium Nostoc sp. strain ATCC 29133.

Heterocysts, sites of nitrogen fixation in certain filamentous cyanobacteria, are limited to a heterotrophic metabolism, rather than the photoautotrophic metabolism characteristic of cyanobacterial vegetative cells. The metabolic route of carbon catabolism in the supply of reductant to nitrogenase and for respiratory electron transport in heterocysts is unresolved. The gene (zwf) encoding glucose-6-phosphate dehydrogenase (G6PD), the initial enzyme of the oxidative pentose phosphate pathway, was inactivated in the heterocyst-forming, facultatively heterotrophic cyanobacterium, Nostoc sp. strain ATCC 29133. The zwf mutant strain had less than 5% of the wild-type apparent G6PD activity, while retaining wild-type rates of photoautotrophic growth with NH4+ and of dark O2 uptake, but it failed to grow either under N2-fixing conditions or in the dark with organic carbon sources. A wild-type copy of zwf in trans in the zwf mutant strain restored only 25% of the G6PD specific activity, but the defective N2 fixation and dark growth phenotypes were nearly completely complemented. Transcript analysis established that zwf is in an operon also containing genes encoding two other enzymes of the oxidative pentose phosphate cycle, fructose-1,6-bisphosphatase and transaldolase, as well as a previously undescribed gene (designated opcA) that is cotranscribed with zwf. Inactivation of opcA yielded a growth phenotype identical to that of the zwf mutant, including a 98% decrease, relative to the wild type, in apparent G6PD specific activity. The growth phenotype and lesion of G6PD activity in the opcA mutant were complemented in trans with a wild-type copy of opcA. In addition, placement in trans of a multicopy plasmid containing the wild-type copies of both zwf and opcA in the zwf mutant resulted in an approximately 20-fold stimulation of G6PD activity, relative to the wild type, complete restoration of nitrogenase activity, and a slight stimulation of N2-dependent photoautotrophic growth and fructose-supported dark growth. These results unequivocally establish that G6PD, and most likely the oxidative pentose phosphate pathway, represents the essential catabolic route for providing reductant for nitrogen fixation and respiration in differentiated heterocysts and for dark growth of vegetative cells. Moreover, the opcA gene product is involved by an as yet unknown mechanism in G6PD synthesis or catalytic activity.

Cell Division↗
PubMed1998

Complex metabolic phenotypes caused by a mutation in yjgF, encoding a member of the highly conserved YER057c/YjgF family of proteins.

The oxidative pentose phosphate pathway is required for function of the alternative pyrimidine biosynthetic pathway, a pathway that allows thiamine synthesis in the absence of the PurF enzyme in Salmonella typhimurium. Mutants that no longer required function of the oxidative pentose phosphate pathway for thiamine synthesis were isolated. Further phenotypic analyses of these mutants demonstrated that they were also sensitive to the presence of serine in the medium, suggesting a partial defect in isoleucine biosynthesis. Genetic characterization showed that these pleiotropic phenotypes were caused by null mutations in yjgF, a previously uncharacterized open reading frame encoding a hypothetical 13.5-kDa protein. The YjgF protein belongs to a class of proteins of unknown function that exhibit striking conservation across a wide range of organisms, from bacteria to humans. This work represents the first detailed phenotypic characterization of yjgF mutants in any organism and provides important clues as to the function of this highly conserved class of proteins. Results also suggest a connection between function of the isoleucine biosynthetic pathway and the requirement for the pentose phosphate pathway in thiamine synthesis.

Amino Acid Sequence↗
PubMed1964

Carbohydrate and lipid content of radiation-resistant and -sensitive strains of Escherichia coli.

Woodside, E. E. (U.S. Army Medical Research Laboratory, Fort Knox, Ky.), and W. Kocholaty. Carbohydrate and lipid content of radiation-resistant and -sensitive strains of Escherichia coli. J. Bacteriol. 87:1140-1146. 1964.-Total lipid contents of acetate minimal medium cultures of Escherichia coli, strains B, B/r, and B(s), were not significantly different when identical pretreatment and extraction procedures were compared. Wide variations in intracellular hexose and pentose derivatives of E. coli B, B/r, and B(s) were induced by changes in carbon and nitrogen sources and by changes in the growth phases. The three strains produced more intracellular carbohydrate when grown in nutrient broth-glucose medium than when grown in unsupplemented nutrient broth. Acetate minimal medium cultures of the radiation-sensitive mutant, E. coli B(s), contained the least, and the radiation-resistant mutant, E. coli B/r the largest, amounts of intracellular hexoses. Environmental conditions which increased the radiation resistance of E. coli B/r were similar to the environmental conditions which favored increased intracellular hexose accumulation. After X ray of E. coli B/r, considerable amounts of hexoses and pentoses were released into the growth medium. Alterations in hexose distribution patterns of X-rayed E. coli B/r preceded alterations in pentose distribution patterns. Prolonged postirradiation incubation resulted in a net synthesis of extracellular hexose, with concomitant loss of intracellular hexose accumulation.

Acetates↗
PubMed1965

POLYOL METABOLISM IN THE BASIDIOMYCETE SCHIZOPHYLLUM COMMUNE.

Niederpruem, Donald J. (Indiana University Medical Center, Indianapolis), Amtul Hafiz, and Lyle Henry. Polyol metabolism in the basidiomycete Schizophyllum commune. J. Bacteriol. 89:954-959. 1965.-The polyol metabolism of intact cells and extracts of the wood-rotting mushroom Schizophyllum commune was investigated during the developmental cycle. Exogenous polyols stimulated the cellular respiration of germlings, but were without effect on that of ungerminated basidiospores. Requisite enzymes of polyol metabolism were demonstrated in extracts of spores and of subsequent stages of development. Oxidation of mannitol and sorbitol appeared to be coupled to nicotinamide adenine dinucleotide (NAD) reduction and was favored in alkaline medium. Ketohexose formation was shown during mannitol oxidation, and the NAD-dependent oxidation of xylitol yielded ketopentose. Xylitol oxidation with nicotinamide adenine dinucleotide phosphate (NADP) as hydrogen acceptor led to pentose formation. Oxidation of reduced NAD was enhanced by fructose but not by sorbose. Reduction of aldohexose and pentose was dependent upon reduced NADP, and pentose reductase was maximal at pH 6.8. The specific activity of mannitol dehydrogenase was highest in extracts of vegetative mycelium. Growth in either glucose or xylose media had no significant effect on enzymes of polyol metabolism.

Alcohols↗
PubMed2005

Thiol oxidation inhibits nitric oxide-mediated pulmonary artery relaxation and guanylate cyclase stimulation.

The mechanisms through which thiol oxidation and cellular redox influence the regulation of soluble guanylate cyclase (sGC) are poorly understood. This study investigated whether promoting thiol oxidation via inhibition of NADPH generation by the pentose phosphate pathway (PPP) with 1 mM 6-aminonicotinamide (6-AN) or the thiol oxidant diamide (1 mM) alters sGC activity and cGMP-associated relaxation to nitric oxide (NO) donors [S-nitroso-N-acetylpenicillamine (SNAP) and spermine-NONOate]. Diamide and 6-AN inhibited NO-elicited relaxation of endothelium-denuded bovine pulmonary arteries (BPA) and stimulation of sGC activity in BPA homogenates. Treatment of BPA with the thiol reductant DTT (1 mM) reversed inhibition of NO-mediated relaxation and sGC stimulation by 6-AN. The increase in cGMP protein kinase-associated phosphorylation of vasodilator-stimulated phosphoprotein on Ser239 elicited by 10 microM SNAP was also inhibited by diamide. Activation of sGC by SNAP was attenuated by low micromolar concentrations of GSSG in concentrated, but not dilute, homogenates of BPA, suggesting that an enzymatic process contributes to the actions of GSSG. Relaxation to agents that function through cAMP (forskolin and isoproterenol) was not altered by inhibition of the pentose phosphate pathway or diamide. Thus a thiol oxidation mechanism controlled by the regulation of thiol redox by NADPH generated via the pentose phosphate pathway appears to inhibit sGC activation and cGMP-mediated relaxation by NO in a manner consistent with its function as an important physiological redox-mediated regulator of vascular function.

Animals↗
PubMed2004

Transaldolase of Methanocaldococcus jannaschii.

The Methanocaldococcus jannaschii genome contains putative genes for all four nonoxidative pentose phosphate pathway enzymes. Open reading frame (ORF) MJ0960 is a member of the mipB/talC family of 'transaldolase-like' genes, so named because of their similarity to the well-characterized transaldolase B gene family. However, recently, it has been reported that both the mipB and the talC genes from Escherichia coli encode novel enzymes with fructose-6-phosphate aldolase activity, not transaldolase activity (Schürmann and Sprenger 2001). The same study reports that other members of the mipB/talC family appear to encode transaldolases. To confirm the function of MJ0960 and to clarify the presence of a nonoxidative pentose phosphate pathway in M. jannaschii, we have cloned ORF MJ0960 from M. jannaschii genomic DNA and purified the recombinant protein. MJ0960 encodes a transaldolase and displays no fructose-6-phosphate aldolase activity. It etained full activity for 4 h at 80 degrees C, and for 3 weeks at 25 degrees C. Methanocaldococcus jannaschii transaldolase has a maximal velocity (Vmax) of 1.0 +/- 0.2 micromol min(-1) mg(-1) at 25 degrees C, whereas Vmax = 12.0 +/- 0.5 micromol min(-1) mg(-1) at 50 degrees C. Apparent Michaelis constants at 50 degrees C were Km = 0.65 +/- 0.09 mM for fructose-6-phosphate and Km = 27.8 +/- 4.3 microM for erythrose-4-phosphate. When ribose-5-phosphate replaced erythrose-4-phosphate as an aldose acceptor, Vmax decreased twofold, whereas the Km was 150-fold higher. The molecular mass of the active enzyme is 271 +/- 27 kDa as estimated by gel filtration, whereas the predicted monomer size is 23.96 kDa, suggesting that the native form of the protein is probably a decamer. A readily available source of thermophilic pentose phosphate pathway enzymes including transaldolase may have direct application in enzymatic biohydrogen production.

Aldehyde-Lyases↗
PubMed1994

Microcytophotometric analysis of human osteoclast metabolism: lack of activity in certain oxidative pathways indicates inability to sustain biosynthesis during resorption.

It has been proposed that highly biosynthetic cells oxidize fatty acids to generate ATP while maintaining high levels of glucose metabolism through the glycolytic and pentose shunt systems to supply biosynthetic intermediates. We investigated the metabolic strategies and substrate for ATP production in the osteoclast. We used in situ quantitative microcytophotometric techniques to determine the maximal activity of the pentose shunt (glucose-6-phosphate dehydrogenase; G6PD), the glycolytic pathway (glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase; G3PD and LDH), fatty acid oxidation (beta-hydroxyacyl dehydrogenase; HOAD), and the Krebs cycle (succinate dehydrogenase; SDH) in human osteoclasts in situ, and related these enzyme activities to the degree of involvement of the cells in resorption. Unlike other highly biosynthetic cells, such as chondrocytes and macrophage polykaryons, osteoclasts associated with bone resorption were deficient in G3PD, LDH, and G6PD activity. However, osteoclasts did demonstrate a capacity for fatty acid oxidation which increased in cells apposed to the bone surface. The lack of significant glycolytic and pentose shunt activity in the osteoclast provides good evidence that resorbing osteoclasts, unlike phagocytosing macrophage polykaryons, have the metabolic characteristics of cells with greatly reduced capabilities of de novo mRNA synthesis but which do maintain high rates of ATP production. The possibility that the loss of glycolytic activity is a prelude to cell death is discussed.

Adenosine Triphosphate↗
PubMed1986

Glucose, acetate, and lactate metabolism in perirenal adipose tissue of fetal and newborn calves.

Rates of utilization of glucose, acetate, and lactate and activities of selected enzymes were determined in vitro to characterize the nature of lipogenesis and metabolite utilization in perirenal adipose tissue from 6- to 7-month old fetal and 3- to 4-h-old unsuckled newborn calves. Contribution of the pentose phosphate cycle to glucose metabolism was estimated using specifically labeled glucose. Rates of fatty acid synthesis from all three substrates and oxidation of glucose were much greater in fetal than in newborn adipose tissue. In fetal adipose tissue, acetate and lactate were major sources of carbon for fatty acid synthesis; glucose functioned mainly by metabolism via the pentose phosphate cycle to provide reducing equivalents for fatty acid synthesis and by incorporation into glyceride glycerol for fatty acid esterification. Pentose phosphate cycle contributed 58 and 12% to glucose metabolism in adipose tissue of fetal and newborn calves, respectively. Adipose tissue metabolism of newborn calves was characterized by greatly depressed rates of fatty acid synthesis despite high enzyme activities and elevated rates of glyceride glycerol synthesis.

Acetates↗
PubMed1990

Effect of low temperatures on glucose-induced insulin secretion and glucose metabolism in isolated pancreatic islets of the rat.

The direct effect of hypothermia on the inhibition of insulin secretion may result from inhibition of the availability of energetic substrates and/or the lack of metabolic signals. In order to verify this hypothesis, the insulin secretion and the main metabolic glucose pathways were measured during the incubation of rat islets. In the presence of 16.7 mmol glucose/l and at 37 degrees C, insulin secretion was 925 +/- 119 microU/2 h per ten islets. With the same experimental conditions, glucose utilization, determined as the formation of 3H2O from [5-3H]glucose was 2225 +/- 184 pmol/2 h per ten islets, glucose oxidation measured as the formation of 14CO2 from [U-14C]glucose was 673 +/- 51 pmol/2 h per ten islets, pentose cycle determined as the formation of 14CO2 from either [1-14C]glucose or [6-14C]glucose was 37 +/- 5 pmol/2 h per ten islets; glucose oxidation by the tricarboxilic acid cycle, calculated to be the difference between glucose oxidation and pentose cycle values, was 636 pmol/2 h per ten islets. Hypothermia highly inhibited glucose-induced insulin secretion and glucose utilization. Inhibition of insulin secretion was partial at 27 degrees C since it was 2.5 times lower than that at 37 degrees C, and it was complete at 17 degrees C. Glucose oxidation in the tricarboxilic acid cycle was markedly inhibited by hypothermia since the inhibition coefficient (Q10) between 37 and 27 degrees C was 5. In contrast, glucose oxidation in the pentose phosphate shunt was enhanced at 27 degrees C, reaching 92 +/- 17 pmol/2 h per ten islets, and it was inhibited relatively little at 17 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗