scispace - formally typeset
Search or ask a question

Showing papers on "Pyruvate kinase published in 1993"


Journal ArticleDOI
TL;DR: In isolated hepatocytes from fasted rats, a significant inhibition of glucose production from lactate/pyruvate, fructose, alanine or glutamine, following metformin addition is observed, and this could explain the stimulation of pyruVate-kinase activity following met formin addition and thus the inhibition of gluconeogenesis.
Abstract: Metformin (dimethylbiguanide) has been used for more than 30 years as an antihyperglycemic agent in the treatment of diabetes mellitus, but its effect on gluconeogenesis is still controversial. In isolated hepatocytes from fasted rats, a significant inhibition of glucose production from lactate/pyruvate (10:1, mol/mol), fructose, alanine or glutamine, following metformin addition, is observed. Moreover, in hepatocytes perifused with dihydroxyacetone as the gluconeogenic substrate and treated with 0.5 mM metformin, an inhibition of the glucose flux and a simultaneous stimulation of the lactate/pyruvate flux were observed. This enhancement of lactate/pyruvate formation appears to be due to an effect on the pyruvate-kinase enzyme. A direct effect of metformin on pyruvate kinase cannot explain this result, since pyruvate-kinase activity was not affected by metformin at this concentration. In contrast, the addition of metformin caused a significant decrease in the cellular ATP concentration, a known allosteric inhibitor of this enzyme. This could explain the stimulation of pyruvate-kinase activity following metformin addition and thus the inhibition of gluconeogenesis.

149 citations


Journal ArticleDOI
TL;DR: The factor that recognizes the PK MLTF-like site and participates in mediating the carbohydrate response of the L-PK gene appears to be a member of the c-myc family distinct from MLTF.

130 citations


Journal ArticleDOI
S Marie1, M J Diaz-Guerra1, L Miquerol1, A Kahn1, Patrick B. Iynedjian1 
TL;DR: The L-type pyruvate kinase gene provides an interesting model of glucose-regulated gene in the endocrine beta-cell type and is shown to increase 4-fold at maximal stimulation, suggesting that both transcriptional and post-transcriptional effects contribute to mRNA accumulation.

122 citations


Journal ArticleDOI
01 Jun 1993-Planta
TL;DR: It is argued that sucrose mobilisation via a reversible reaction catalysed by sucrose synthase is particularily well suited to allow the rate of sucrose breakdown in the phloem to respond to changes in the metabolic requirement for ATP, and for UDPGlc during callose production.
Abstract: Metabolites and enzyme activities were measured in the phloem sap exuding from a cut hypocotyl of germinating castor-bean (Ricinus communis L.) seedlings. The sap contained considerable quantities of adenine nucleotides, uridine nucleotides, uridine diphosphoglucose (UDPGlc), all the major phosphorylated metabolites required for glycolysis, fructose-2,6-bisphosphate and pyrophosphate. Supplying 200 mM glucose instead of sucrose to the cotyledons resulted in high concentrations of glucose in the sap, but did not modify the metabolite levels. In contrast, when 200 mM fructose was supplied we found only a low level of fructose but a raised sucrose concentration in the sap, which was accompanied by a three-to fourfold decrease of UDPGlc, and an increase of pyrophosphate, UDP and UTP. The measured levels of metabolites are used to estimate the molar mass action ratios and in-vivo free-energy change associated with the various reactions of sucrose breakdown and glycolysis in the phloem. It is concluded that the reactions catalysed by ATP-dependent phosphofructokinase and pyruvate kinase are removed from equilibrium in the phloem, whereas the reactions catalysed by sucrose synthase, UDPGlc-pyrophosphorylase, phosphoglucose mutase, phosphoglucose isomerase, aldolase, triose-phosphate isomerase, phosphoglycerate mutase and enolase are close to equilibrium within the conducting elements of the phloem. Since the exuded sap contained negligible or undetectable activities of the enzymes, it is concluded, that the responsible proteins are bound, or sequesterd behind plasmodesmata, possibly in the companion cells. It is argued that sucrose mobilisation via a reversible reaction catalysed by sucrose synthase is particularily well suited to allow the rate of sucrose breakdown in the phloem to respond to changes in the metabolic requirement for ATP, and for UDPGlc during callose production. It is also calculated that the transport of nucleotides in the phloem sap implies that there must be a very considerable uptake or de-novo biosynthesis of these cofactors in the phloem.

116 citations


Journal ArticleDOI
TL;DR: The enrichment and isotopomer pattern in the lactate from cleaved glucose represents that in phosphoenolpyruvate (PEP), and it appears that the glutamates are derived from alpha-ketoglutarate from a different Krebs cycle pool than PEP.

115 citations


Journal ArticleDOI
TL;DR: The discovery of a novel multicistronic operon that encodes phosphofructokinase, pyruvate kinase, and lactate dehydrogenase in the lactic acid bacterium Lactococcus lactis is reported, which is called the las (lactic acid synthesis) operon.
Abstract: The discovery of a novel multicistronic operon that encodes phosphofructokinase, pyruvate kinase, and lactate dehydrogenase in the lactic acid bacterium Lactococcus lactis is reported. The three genes in the operon, designated pfk, pyk, and ldh, contain 340, 502, and 325 codons, respectively. The intergenic distances are 87 bp between pfk and pyk and 117 bp between pyk and ldh. Plasmids containing pfk and pyk conferred phosphofructokinase and pyruvate kinase activity, respectively, on their host. The identity of ldh was established previously by the same approach (R. M. Llanos, A. J. Hillier, and B. E. Davidson, J. Bacteriol. 174:6956-6964, 1992). Each of the genes is preceded by a potential ribosome binding site. The operon is expressed in a 4.1-kb transcript. The 59 end of the transcript was determined to be a G nucleotide positioned 81 bp upstream from the pfk start codon. The pattern of codon usage within the operon is highly biased, with 11 unused amino acid codons. This degree of bias suggests that the operon is highly expressed. The three proteins encoded on the operon are key enzymes in the Embden-Meyerhoff pathway, the central pathway of energy production and lactic acid synthesis in L. lactis. For this reason, we have called the operon the las (lactic acid synthesis) operon. Images

88 citations


Journal ArticleDOI
01 Jul 1993-Yeast
TL;DR: Increase in the level of fructose‐2, 6‐bisphosphate is demonstrated to depend on an internal metabolite upstream of the phosphoglucose isomerase reaction, indicating an adaptational mechanism.
Abstract: The glycolytic pathway in Saccharomyces cerevisiae is activated by fermentable sugars at several steps. Mutants with deletions of genes coding for enzymes of the upper part of glycolysis were used to characterize the triggering mechanisms. Synthesis of fructose-2,6-bisphophate is catalysed by two 6-phosphofructo-2-kinase isoenzymes, one of which is activated by fermentable sugars while synthesis of the second enzyme is induced (Kretschmer and Fraenkel, 1991). Increase in the level of fructose-2,6-bisphosphate is demonstrated to depend on an internal metabolite upstream of the phosphoglucose isomerase reaction. The signalling process correlates with distinct temporal changes in the concentration of glucose-6-phosphate but not with its absolute level, indicating an adaptational mechanism. It is independent of the uptake and phosphorylation systems used by different sugars. Interestingly, this increase, although delayed, could also be observed in strains lacking the rapid cAMP increase after sugar addition which is thought to be responsible for the activating process. Synthesis of glucose-6-P and fructose-6-P is needed for the complete induction of pyruvate kinase and inactivation of fructose-1,6-bisphosphatase. On the other hand, induction of pyruvate decarboxylase depends mainly on a signal in the lower part of glycolysis.

86 citations


Journal ArticleDOI
TL;DR: Increased maximum catalytic activities were found for sucrose synthase, PFK(PP i ) (× 6), pyruvate kinase, alcohol dehydrogenase (× 5) and lactate dehydrogenases (× 2), when rice cells were grown in anoxia, respiration declined steadily and fermentation declined steadily.

79 citations


Journal ArticleDOI
TL;DR: Oral vanadate given to diabetic rats induces a shift of the predominating gluconeogenic flux, with subsequent high hepatic glucose production, into a glycolytic flux by pretranslational regulatory mechanisms.

74 citations


Journal ArticleDOI
TL;DR: Results suggest that the regulation of the expression of genes involved in the glucose and ketone bodies metabolism could be a key step in the normalization process induced by vanadate administration to diabetic rats.
Abstract: Oral administration of vanadate to diabetic streptozotocin-treated rats decreased the high blood glucose and D-3-hydroxybutyrate levels related to diabetes. The increase in the expression of the P-enolpyruvate carboxykinase (PEPCK) gene, the main regulatory enzyme of gluconeogenesis, was counteracted in the liver and the kidney after vanadate administration to diabetic rats. Vanadate also counteracted the induction in tyrosine aminotransferase gene expression due to diabetes and was able to increase the expression of the glucokinase gene to levels even higher than those found in healthy animals. Similarly, an induction in pyruvate kinase mRNA transcripts was observed in diabetic vanadate-treated rats. These effects were correlated with changes on glucokinase and pyruvate kinase activities. Vanadate treatment caused a decrease in the expression of the liver-specific glucose transporter, GLUT-2. Thus, vanadate was able to restore liver glucose utilization and block glucose production in diabetic rats. The increase in the expression of the mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCoAS) gene, the key regulatory enzyme in the ketone bodies production pathway, observed in diabetic rats was also blocked by vanadate. Furthermore, a similar pattern in the expression of PEPCK, GLUT-2, HMGCoAS, and the transcription factor CCAAT/enhancer-binding protein alpha genes has been observed. All of these results suggest that the regulation of the expression of genes involved in the glucose and ketone bodies metabolism could be a key step in the normalization process induced by vanadate administration to diabetic rats.

73 citations


Journal ArticleDOI
TL;DR: The intron sequences of the human L-type pyruvate kinase gene (PKLR) were determined by using primers selected from the known cDNA sequence, and the context with respect to a polymorphism at nt 1705 was compatible with a single origin for this mutation.
Abstract: The intron sequences of the human L-type pyruvate kinase gene (PKLR) were determined by using primers selected from the known cDNA sequence. Oligonucleotide primers for these determined intron sequences were used to sequence the exons. When this technique was applied to the DNA of 10 unrelated patients with pyruvate kinase deficiency, the following eight different mutations in the coding region were detected: del391-393, A401, C464, G721, A1076, T1456, T1484, A1529. The A1529 mutation was found repeatedly in unrelated individuals, even in the homozygous state. The context with respect to a polymorphism at nt 1705 was compatible with a single origin for this mutation, and it may represent a balanced polymorphism. In normal subjects, five differences from the published cDNA sequence were documented.

Journal ArticleDOI
TL;DR: The presence of phosphoenolpyruvate (PEP) carboxylase, an enzyme at the branchpoint of glycolysis and the Krebs cycle was detected in the Filaria Molinema dessetae, and when purified to electrophoretic homogeneity, the enzyme had a molecular weight of 64 kDa.
Abstract: The presence of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31), an enzyme at the branchpoint of glycolysis and the Krebs cycle was detected in the Filaria Molinema dessetae. This enzyme has not previously been identified in Helminths, which have so far been found to only possess a phosphoenolpyruvate carboxykinase (EC 4.1.1.32). This enzyme had a level of activity comparable to that of pyruvate kinase, and was relatively less active than enzymes such as malate dehydrogenase or lactate dehydrogenase. We propose here a method of purification of M. dessetae PEP-carboxylase. When purified to electrophoretic homogeneity, the enzyme had a molecular weight of 64 kDa. Kinetic studies indicated that the carboxylation reaction had an optimal pH of 5.8. The enzyme was inhibited by cations such as Fe2+, Zn2+, Cd2+, Cu2+ but required the presence of Mg2+ or Mn2+. The enzyme was thermostable. The apparent Km value of 2.38 mmol for phosphoenolpyruvate for the carboxylation reaction was higher than previously reported values. The Km value for KHCO3 was found to be 1.6 mmol. PEP-carboxylase did not catalyse the reverse reaction.

Journal ArticleDOI
TL;DR: PDCase levels in glycolysis mutant strains growing on ethanol or acetate were higher than in the wild-type strain, interpreted to mean that full induction of PDCase activity requires the accumulation of hexose-and triosephosphates.
Abstract: Pyruvate decarboxylase, PDCase, activity in wild-type yeast cells growing on ethanol is quite low but increases up to tenfold upon addition of glucose, less with galactose and only slightly with glycerol. PDCase levels in glycolysis mutant strains growing on ethanol or acetate were higher than in the wild-type strain. These levels correlated with the sum of the concentrations of three-carbon glycolytic metabolites. The highest accumulation was observed in a fructose bisphosphate aldolase deletion mutant concomintant with the highest PDCase activity wild-type level. On the other hand, the PDCase levels in the different mutants again correlated with the sum of the concentrations of the three-carbon glycolytic metabolites. This was interpreted to mean that full induction of PDCase activity requires the accumulation of hexose-and triosephosphates.


Journal ArticleDOI
TL;DR: The homology of the sequence showed that the gene encodes phosphofructokinase, which was expressed in E. coli cells, and the evidence suggesting that both genes constitute an operon is presented.
Abstract: Pyruvate kinase from Bacillus stearothermophilus is an allosteric enzyme activated by AMP or ribose 5-phosphate but not by fructose 1,6-bisphosphate. The gene for the enzyme was cloned in Escherichia coli and its entire nucleotide sequence was determined. The deduced amino acid sequence consisted of 587 residues and the molecular mass was calculated to be 62 317 Da. The sequence was highly similar to other pyruvate kinases, indicating that they have the same evolutional origin. Similarly to the E. coli enzymes, the enzyme does not contain an N-terminal domain, in contrast to the eukaryotic pyruvate kinases. However, the Bacillus stearothermophilus enzyme had an extra C-terminal sequence consisting of about 110 amino acid residues. A phosphoenolpyruvatebinding motif, which is observed in pyruvate phosphate dikinase, phosphoenolpyruvate: sugar phosphotransferase system enzyme I and phosphoenolpyruvate synthase, was present in the extra C-terminal sequence. There was an open reading frame upstream of the pyruvate kinase gene. The homology of the sequence showed that the gene encodes phosphofructokinase. Both phosphofructokinase and pyruvate kinase were expressed in E. coli cells, and the evidence suggesting that both genes consitute an operon is presented.

Journal ArticleDOI
TL;DR: In this article, a pyruvate kinase deficiency was diagnosed in an infant by umbilical vessel sampling at 30 weeks' gestation and the infant survived with transfusion dependent haemolytic anaemia.
Abstract: Pyruvate kinase deficiency was diagnosed in an infant by umbilical vessel sampling at 30 weeks' gestation. Although three previous hydropic siblings had been stillborn or died in the neonatal period, this infant survived with transfusion dependent haemolytic anaemia. Prompt fetal diagnosis of pyruvate kinase deficiency is feasible and allows better management of hydrops fetalis due to this disorder.

Journal ArticleDOI
TL;DR: The effects of phenylethylbiguanide (phenformin) on the rate of gluconeogenesis and metabolite profiles in the perfused liver are similar to those caused by DCMU, supporting a mitochondrial locus of action for this hypoglycaemic agent.

Journal Article
TL;DR: Results from Northern blot analysis indicate that the expression of the T antigen gene (Tag) is dependent on the concentration of D-glucose in the medium and show that the L-PK construct has maintained its capacity for up- or down-regulation by carbohydrates.
Abstract: This study describes the functional characterization of two cell lines derived from the proximal convoluted (PKSV-PCT cells) and proximal straight (PKSV-PR) tubules microdissected out from kidneys of transgenic mice harboring the simian virus 40 (SV40) large T and small t antigens placed under the control of the rat Ltype pyruvate kinase (L-PK) 5 regulatory sequence. Both cell lines exhibited cellular cyclic AMP stimulated by parathormone (PTH) and calcitonin (CT) and a sodium-dependent glucose transporter. Uptake of the fluid-phase marker [ 3 H]inulin showed that both cell lines grown on filters exhibited biphasic apical and basolateral endocytic rates. Results from Northern blot analysis indicate that the expression of the T antigen gene (Tag) is dependent on the concentration of D-glu cose in the medium and show that the L-PK construct has maintained its capacity for up- or down-regulati on by carbohydrates. Replacement of D-glucose by neoglucogenic substrates (lactate, oxaloacetate) blunted the expression of Tag transcripts and induced arrest of cell growth. Compared to cell grown in D-glucoseenriched medium, the hormonal sensitivities to PTH and CT and the sodium-dependent glucose uptake were unchanged whereas quiescent cells exhibited increased hydrolase content. Thus the proximal function has been preserved in these cultured cells derived from tissuespecific targeted oncogenesis in transgenic mice. As the expression of Tag transcripts is controlled by D-glucose, the structural and physiological characteristics of these cell lines can be studied in either quiescent or active growth conditions. SUMMARY

Journal ArticleDOI
TL;DR: The lipoyl prosthetic group on one of the twolipoyl domains of E2 subunits is critically important for maintaining E2-activated kinase function and contributes to binding of the kinase to E2.

Journal ArticleDOI
TL;DR: In this article, a d -tagatose 1,6-bisphosphate aldolase requiring Zn 2+ for catalytic activity (class II) was purified from E. coli cells grown on galactitol.

Journal ArticleDOI
TL;DR: Treatment of 18 h-starved rats with dexamethasone and subsequent isolation and incubation of the hepatocytes in the presence of the steroid increased gluconeogenic flux with both pyruvate kinase flux and glucose synthesis with both substrates employed, indicating that the steroid had no effect on the partitioning of phosphoenolpyruvates between pyruVate and lactate formation and gluconeogenesis.
Abstract: Treatment of 18 h-starved rats with dexamethasone and subsequent isolation and incubation of the hepatocytes in the presence of the steroid increased gluconeogenic flux with both 1.0 mM pyruvate and 1.0 mM lactate plus 0.2 mM pyruvate as the substrate. The magnitude of stimulation was comparable with both substrates. The increase in glucose output was accompanied by an increased flux through pyruvate carboxylase, although the absolute flux and magnitude were considerably less in the presence of the more reduced substrate. The effect of the steroid on the flux through pyruvate dehydrogenase was substrate-dependent, an inhibition occurring with the more oxidized substrate. There was no effect of steroid treatment on [1-14C]lactate or pyruvate oxidation or on tricarboxylic-acid-cycle flux as measured by [3-14C]pyruvate oxidation. Dexamethasone treatment resulted in a parallel increase in both pyruvate kinase flux and glucose synthesis with both substrates employed, indicating that the steroid had no effect on the partitioning of phosphoenolpyruvate between pyruvate and lactate formation and gluconeogenesis. Similarly there was no effect of the steroid on either the activity ratio or the total pyruvate kinase activity in the cells. It is suggested that the acute effect of the dexamethasone to increase gluconeogenesis resides at the level of phosphoenolpyruvate formation, i.e. pyruvate carboxylase and possibly phosphoenolpyruvate carboxykinase.

Journal ArticleDOI
TL;DR: A fragment of 1,185 bp containing the gene coding for phosphofructokinase in Lactobacillus bulgaricus has been cloned, sequenced, and expressed in Escherichia coli, suggesting that these enzymes have closely related structures despite their different regulatory properties.
Abstract: A fragment of 1,185 bp containing the gene coding for phosphofructokinase (ATP:D-fructose-6-phosphate-1-phosphotransferase; EC 2.7.1.11) in Lactobacillus bulgaricus has been cloned, sequenced, and expressed in Escherichia coli. The amino acid sequence of this enzyme was homologous to those of the ATP-dependent phosphofructokinases from E. coli, Thermus thermophilus, Spiroplasma citri, and Bacillus stearothermophilus, suggesting that these enzymes have closely related structures despite their different regulatory properties. The recombinant protein had the same structural and functional properties as did the original enzyme. The 3' end of the 1,185-bp fragment showed the presence of an open reading frame corresponding to the N-terminal amino acid sequence of the pyruvate kinase from L. bulgaricus. This gene organization, the same as that in S. citri (C. Chevalier, C. Saillard, and J. M. Bove, J. Bacteriol. 172:2693-2703, 1990) and B. stearothermophilus (D. Walker, W. N. Chia, and H. Muirhead, J. Mol. Biol. 228:265-276, 1992; H. Sakai and T. Ohta, Eur. J. Biochem. 311:851-859, 1993) but different from that in E. coli (H. W. Hellinga and P. R. Evans, Eur. J. Biochem. 149:363-373, 1985), indicated that the same transcription unit apparently contained the genes for phosphofructokinase and pyruvate kinase, the two key enzymes of glycolysis. The possibility that these genes could be transcribed at the same time suggested that in L. bulgaricus, the coordinated regulation of phosphofructokinase and pyruvate kinase occurs at the levels of both biosynthesis and enzymatic activity.

Journal ArticleDOI
01 May 1993-Blood
TL;DR: A point mutation was identified in the R-type pyruvate kinase (PK) cDNA of a PK variant, PK Sapporo, associated with hereditary non-spherocytic hemolytic anemia, and it has been proposed that this region as well as A alpha 7, A beta 7, and A beta 8 is a potassium (K+) binding site.

Journal ArticleDOI
TL;DR: The isolation of a pyruvate kinase cDNA clone from soybean somatic embryos is reported, indicating that there is probably a single gene for this pyruve kinase in soybean.
Abstract: Pyruvate kinase (EC 2.7.1.40) is one of the key regulatory enzymes controlling glycolysis in plants and animals. It catalyzes the irreversible formation of pyruvate and ATP from phosphoenolpyruvate and ADP. In plants, pyruvate kinases can be either heteroor homotetramers depending on the source of the isozyme (Plaxton, 1989). Pyruvate kinase enzymes have been purified or partially purified from severa1 plant species (Plaxton, 1988); however, the gene encoding pyruvate kinase has been isolated only from Ricinus communis (Blakeley et al., 1991) and Solanum tuberosum (Blakeley et al., 1990). Here, we report the isolation of a pyruvate kinase cDNA clone from soybean (Glycine max [L.] Merr.) somatic embryos. A XgtlO cDNA library was constructed from poly(A’) RNA of proliferating globular-stage somatic embryos. The pyruvate kinase cDNA (Table I) was initially isolated by differential hybridization based on higher expression in globular embryos than in cotyledon embryos. Excluding the polyadenylation tail, the cDNA is 1795 b p long and contains a n open reading frame of 1533 nucleotides (predicted protein of 511 amino acids) and a 61-nucleotide 5’ and a 198-nucleotide 3’ untranslated region. In the 3‘ untranslated region, there is a putative polyadenylation signal, AAATAA, upstream of the polyadenylate sequence. Comparison of the derived protein with data base proteins revealed extensive homology with many nonplant pyruvate kinases. The soybean pyruvate kinase has 89.4% identity with potato pyruvate kinase (Blakeley et al., 1990) and 32.5% identity with pKpa, the castor bean pyruvate kinase (Blakeley et al., 1991). Southern hybridization analysis revealed two bands when genomic DNA was digested with HindIII. Because there is one HindIII site within the cDNA, there is probably a single gene for this pyruvate kinase in soybean. Although differential hybridization indicated that pyruvate kinase mRNA was expressed at a higher leve1 in globular-stage somatic embryos than cotyledon-stage embryos, this was not supported by extensive northem hybridization analysis using RNA from various staged somatic embryos of soybean.

Journal ArticleDOI
22 Dec 1993-Gene
TL;DR: Comparison of the available aa sequences of ATP(protozoa, yeast and bacteria)- and GTP(vertebrates, insects, helminths and fungi)-dependent PEPCKs showed that the former lack two characteristic, highly conserved regions present in the GTP-dependent enzymes.

Journal ArticleDOI
01 Jun 1993-Planta
TL;DR: The results indicate that hexokinase and phosphoglyceromutase are absent from pea root plastids and the possible function of the remaining enzymes is considered.
Abstract: The presence of the glycolytic enzymes from hexokinase to pyruvate kinase in plastids of seedling pea (Pisum sativum L.) roots was investigated. The recoveries, latencies and specific activities of each enzyme in different fractions was compared with those of organelle marker enzymes. Tryptic-digestion experiments were performed on each enzyme to determine whether activities were bound within membranes. The results indicate that hexokinase (EC 2.7.1.2) and phosphoglyceromutase (EC 5.4.2.1) are absent from pea root plastids. The possible function of the remaining enzymes is considered.

Journal ArticleDOI
TL;DR: Findings suggested that both the structural mutation near the active site and the decreased mRNA level of the R-PK were responsible for the disorder.

Journal ArticleDOI
TL;DR: Results suggest that changes in the redox state of cellular microenvironments, which inevitably occur during reperfusion of ischemic tissue or rapid increase in tissue oxygen consumption, may selectively depress the activity of several enzymes bearing SH groups that are sensitive to modifications and that are essential for their activity.

Journal ArticleDOI
TL;DR: It is concluded that estrogen depresses gluconeogenesis and that this reduction contributes to the lower plasma glucose concentration seen in vitellogenic trout.
Abstract: To investigate the effects of estrogen, the hormone responsible for vitellogenesis, on gluconeogenesis, male rainbow trout were implanted with 17 beta-estradiol or given a sham procedure. Plasma glucose concentration in estrogenized fish was 50% of the control fish (6.4 mM). Glucose synthesis from physiological concentrations of alanine was 0.08 mumol.g cells-1 x h-1 compared with 0.20 mumol.g cells-1 x h-1 in control fish; synthesis from physiological concentrations of lactate was reduced by over 50% (0.88 vs. 0.36 mumol.g cells-1 x h-1) in implanted fish. Gluconeogenesis from 5 mM lactate was also significantly depressed in implanted fish. Oxidation of alanine, serine, and lactate was not significantly affected by estrogen implantation. The maximum clearance velocity of a key enzyme negatively regulating gluconeogenesis, pyruvate kinase, was 3.03 mumol.g cells-1 x h-1 in estrogen (E2) implanted fish compared with 7.83 mumol.g cells-1 x h-1 in control fish. No significant differences in plasma insulin or glucagon were found in the two groups. We conclude that estrogen depresses gluconeogenesis and that this reduction contributes to the lower plasma glucose concentration seen in vitellogenic trout.

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the tolerance and responses of mango (Mangifera indica L. var. Keitt) fruits to a modified atmosphere (MA) of 0.03 to 0.26% O2 and 72 to 82% CO2 (balance N2) for 0 to 4 days at 20°C, and to a controlled atmosphere (CA) of 2% O 2 + 50% CO 2 (balance n2), and they concluded that MA and CA delayed fruit ripening.
Abstract: The tolerance and responses of mango (Mangifera indica L. var. Keitt) fruits to a modified atmosphere (MA) of 0.03 to 0.26% O2 and 72 to 82% CO2 (balance N2) for 0 to 4 days at 20°C, and to a controlled atmosphere (CA) of 2% O2 + 50% CO2 (balance N2) for 0 to 5 days at 20°C, were evaluated. MA and CA delayed fruit ripening. Both MA and CA increased the activity of ATP:phosphofructokinase, alcohol dehydrogenase, and pyruvate decarboxylase, but did not affect the activity of pyruvate kinase. MA decreased the activity of PPi:phosphofructokinase. Although the atmospheres used caused changes in the activity of some glycolytic enzymes, there was no indication of any injury and fruits ripened normally. Sensory evaluation did not indicate the presence of off-odours and off-flavours. This work indicates a potential application of MA/CA for post-harvest insect control in mango fruits.