A Kinetic Study of Pyrophosphate: Fructose‐6‐Phosphate Phosphotransferase from Potato Tubers

Schaftingen, Emile Van; Lederer, B; Bartrons, Ramón; Hers, Henri‐Géry

doi:10.1111/j.1432-1033.1982.tb07039.x

Cited by 637 publications

(384 citation statements)

References 21 publications

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“…Glycogen was measured as previously described [24]. Fructose 2,6=bisphosphate was stabi1ized by mixing 0.3 ml of the contents of the incubation vessel with 0.3 ml 0.1 M NaOH and the mixture heated at 80°C for 10 min [25]. Samples were stored at 4'C until assayed.…”

Section: Methodsmentioning

confidence: 99%

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Effects of fatty acid oxidation on glucose utilization by isolated hepatocytes

et al. 1993

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We have studied the inhibitory action of long-and short-chain fatty acids on hepatic glucose utilization in hepatocytes isolated from fasted rats. The rates of hepatic glucose phosphorylation and glycolysis were determined from the tritiated products of [2-'H] and [6-3H]glucose metabolism, respectively. The difference between these was taken as an estimate of the 'cycling' between glucose and glucose-6-phosphate. In the presence of 40 mM glucose this cycling was estimated at 0.68 pmol/min/g wet wt. Glucose phosphorylation was unaffected during palmitate and hexanoate oxidation to ketone bodies but glycolysis was inhibited. The rate of glucose cycling was increased during this phase to 1.25 pmol/min/g. Following the complete metabolism of the fatty acids, glycolysis was reinstated and cycling rates returned to control levels. Hepatic glucose cycling appears to be an important component of the glucose/fatty acid cycle.

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Section: Methodsmentioning

confidence: 99%

“…Samples were stored at 4'C until assayed. A11 extracts were diluted IO-fold with 10 mM NaOH before assay according to Van Schaftingen et al [25]. For the determination of radioactive metabofites, samples (0.5 ml) were deproteinized in I .5 ml of ethanol at 4'C and centrifuged.…”

Section: Methodsmentioning

confidence: 99%

Effects of fatty acid oxidation on glucose utilization by isolated hepatocytes

et al. 1993

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“…Fru-2,6-P 2 was extracted and measured as described by Van Schaftingen et al 23 Total and active PFK-2 activities were measured as described by Bartrons et al 24 In the conditions of the assay, the active form corresponds to the activity of the non-phosphorylated form of the enzyme measured. 24 L-PK activity was determined at saturating concentrations of phosphoenolpyruvate (5 mM), as previously described by Felõ Âu et al 25 and GK as described by Davidson and Arion.…”

Section: Metabolite and Enzyme Assaysmentioning

confidence: 99%

Effect of starvation on gene expression of regulatory enzymes of glycolysis/gluconeogenesis in genetically obese (fa/fa) Zucker rats

et al. 1998

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OBJECTIVE: To study the mechanism that controls fructose-2,6-bisphosphate (Fru-2,6-P 2 ) accumulation, as well as the mRNAs levels of the glycolyticagluconeogenic regulatory enzymes in the livers of fed and starved lean ( faa-) and obese ( faafa) Zucker rats. DESIGN: Rats were fed a standard chow or deprived of food for 24 h. SUBJECTS: Male lean (faa-) and genetically obese ( faafa) rats (nine weeks old). MEASUREMENTS: Fru-2,6-P 2 concentration, 6-phosphofructo-2-kinase (PFK-2), glucokinase (GK), pyruvate kinase (PK) activities and the mRNA levels of GK, PFK-2, L-type pyruvate kinase, fructose-1,6-bisphosphatase (FBPase-1) and phosphoenolpyruvate carboxykinase (PEPCK) were analyzed. RESULTS: PFK-2aFBPase-2 mRNA decreased during starvation in both faa-and faafa animals. Although PFK2aFBPase-2 mRNA levels were similar in fed lean and obese rats, PFK-2 concentration and activity were higher in fed obese than in fed lean animals, which might explain the high concentration of Fru-2,6-P 2 observed in obese animals. During starvation, PFK-2 protein concentration decreased, correlating with the enzymatic activity and Fru-2,6-P 2 levels. The activities of GK and L-pyruvate kinase (L-PK) also increased in fed obese (faafa) rats compared with fed lean (faa-) animals, but decreased during starvation. The mRNA levels of glycolytic enzymes in fed obese rats were similar (PFK-2) or higher than (GK, L-PK) in fed lean animals. During starvation, they decreased in lean and obese rats with one important exception, GK mRNA remained high in obese animals. The mRNA of gluconeogenic enzymes remained constant (FBPase-1) or increased (PEPCK) during fasting. CONCLUSION: The changes observed might be explained by the hyperinsulinaemia observed in the liver of obese rats, which might lead to the stimulation of glycolysis and lipogenesis.

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“…Fru 2,6-P2 was assayed based on the activation of pyrophosphate-dependent fructose-6-phosphate kinase (31). Known amounts of Fru 2,6-P2 were used to obtain a standard curve for the compound in a reaction mixture containing 0.33 unit aldolase, 0.33 unit glycerol phosphate dehydrogenase, 3.3 units triosephospate isomerase, 0.008 unit PPi-phosphofructokinase, the coupling enzymes (Sigma), in addition to 2.5 mm fructose-6-phosphate, 2.5 mm pyrophosphate di- sodium in 50 mM Tris-HCI (pH 8.0), 0.14 mM NADH, and 20 uL solution of Fru 2,6-P2 or plant extracts.…”

Section: Assay Of Fru 26-p2mentioning

confidence: 99%

Acetaldehyde Stimulation of Net Gluconeogenic Carbon Movement from Applied Malic Acid in Tomato Fruit Pericarp Tissue

Halinska¹,

Frenkél²

1991

Plant Physiol.

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Applied acetaldehyde is known to lead to sugar accumulation in fruit including tomatoes (Lycopersicon esculentum) (O Paz, HW Janes, BA Prevost, C Frenkel [1982] presumably due to stimulation of gluconeogenesis. This conjecture was examined using tomato fruit pencarp discs as a test system and applied -[U-14C]malic acid as the source for gluconeogenic carbon mobilization. The label from malate was recovered in respiratory C02, in other organic acids, in ethanol insoluble material, and an appreciable amount in the ethanol soluble sugar fraction. In Rutgers tomatoes, the label recovery in the sugar fraction and an attendant label reduction in the organic acids fraction intensified with fruit ripening. In both Rutgers and in the nonripening tomato rin, these processes were markedly stimulated by 4000 ppm acetaldehyde. The onset of label apportioning from malic acids to sugars coincided with decreased levels of fructose-2,6-biphosphate, the gluconeogenesis inhibitor.In acetaldehyde-treated tissues, with enhanced label mobilization, this decline reached one-half to one third of the initial fructose-2,6-biphosphate levels. Application of 30 micromolar fructose-2,6-biphosphate or 2,5-anhydro-d-mannitol in tum led to a precipitous reduction in the label flow to sugars presumably due to inhibition of fructose-1,6-biphosphatase by the compounds. We conclude that malic and perhaps other organic acids are carbon sources for gluconeogenesis occurring normally in ripening tomatoes. The process is stimulated by acetaldehyde apparently by attenuating the fructose-2,6-biphosphate levels. The mode of the acetaldehyde regulation of fructose-2,6-biphosphate metabolism awaits clarification.AA4 is a common volatile in plants that accumulate during physiological disorders (25) and in ripening fruit (7,14).

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A Kinetic Study of Pyrophosphate: Fructose‐6‐Phosphate Phosphotransferase from Potato Tubers

Cited by 637 publications

References 21 publications

Effects of fatty acid oxidation on glucose utilization by isolated hepatocytes

Effects of fatty acid oxidation on glucose utilization by isolated hepatocytes

Effect of starvation on gene expression of regulatory enzymes of glycolysis/gluconeogenesis in genetically obese (fa/fa) Zucker rats

Acetaldehyde Stimulation of Net Gluconeogenic Carbon Movement from Applied Malic Acid in Tomato Fruit Pericarp Tissue

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