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PubMed1991

Fructose 2,6-bisphosphate and AMP increase the affinity of the Ascaris suum phosphofructokinase for fructose 6-phosphate in a process separate from the relief of ATP inhibition.

Kinetic data have been collected suggesting that heterotropic activation by fructose 2,6-bisphosphate and AMP is a result not only of the relief of allosteric inhibition by ATP but is also the result of an increase in the affinity of phosphofructokinase for fructose 6-phosphate. Modification of the Ascaris suum phosphofructokinase at the ATP inhibitory site produces a form of the enzyme that no longer has hysteretic time courses or homotropic positive (fructose 6-phosphate) cooperativity or substrate inhibition (ATP) (Rao, G.S. J., Wariso, B.A., Cook, P.F., Hofer, H.W., and Harris, B.G. (1987a) J. Biol. Chem. 262, 14068-14073). This form of phosphofructokinase is Michaelis-Menten in its kinetic behavior but is still activated by fructose 2,6-bisphosphate and AMP and by phosphorylation using the catalytic subunit of cyclic AMP-dependent protein kinase (cAPK). Fructose 2,6-bisphosphate activates by decreasing KF-6-P by about 15-fold and has an activation constant of 92 nM, while AMP decreases KF-6-P about 6-fold and has an activation constant of 93 microM. Double activation experiments suggest that fructose 2,6-bisphosphate and AMP are synergistic in their activation. The desensitized form of the enzyme is phosphorylated by cAPK and has an increased affinity for fructose 6-phosphate in the absence of MgATP. The increased affinity results in a change in the order of addition of reactants from that with MgATP adding first for the nonphosphorylated enzyme to addition of fructose 6-phosphate first for the phosphorylated enzyme. The phosphorylated form of the enzyme is also still activated by fructose 2,6-bisphosphate and AMP.

Adenosine Monophosphate↗
PubMed1984

Differences in kinetic properties of phospho and dephospho forms of fructose-6-phosphate, 2-kinase and fructose 2,6-bisphosphatase.

Fructose-6-P,2-kinase:fructose 2,6-bisphosphatase has been purified to homogeneity. The ratio of the activities of fructose-6-P,2-kinase to fructose 2,6-bisphosphatase is 1.2. The enzyme ("native") contains 0.2 mol of phosphate/mol of subunit, and it is fully phosphorylated to 0.96 mol of phosphate/mol of subunit by cAMP-dependent protein kinase. Kinetic behavior of the native and phosphorylated forms of these enzymes was investigated. Both native and phosphofructose-6-P,2-kinase show sigmoidal kinetics with respect to fructose-6-P with an apparent K0.5 of 15 microM and 50 microM, respectively. The Hill coefficients are also increased from 1.3 to 2 by phosphorylation. The initial velocity patterns with respect to ATP follows Michaelis-Menten kinetics but the K0.5 of the phosphoenzyme (0.5 mM) is higher than that of the native enzyme (0.25 mM). The native fructose 2,6-bisphosphatase shows a biphasic saturation curve with respect to fructose-2,6-P2 which appears to be negatively cooperative. The phosphofructose 2,6-bisphosphatase, however, exhibits no cooperativity, and the apparent K0.5 for the substrate is 0.5 microM. Both forms of the phosphatase show the same Vmax. Based on these results possible allosteric regulation of fructose-6-P, 2-kinase and fructose 2,6-bisphosphatase in a reciprocal manner in vivo is discussed.

Adenosine Triphosphate↗
PubMed1983

Chronic fructose intoxication after infancy in children with hereditary fructose intolerance. A cause of growth retardation.

In two unrelated boys, 5.3 and 3.8 years of age with hereditary fructose intolerance, apparently isolated growth retardation (-2.71 S.D. and -2.40 S.D.) occurred after infancy, even though acute symptomatic fructose intoxication was prevented by restriction of dietary fructose. When more stringent restriction of dietary fructose was instituted (approximately 40 mg per kilogram of body weight per day), growth velocity increased from the 25th to the 97th percentile in one child and from well below the 3d to above the 75th percentile in the other. When restriction of dietary fructose was experimentally relaxed (from 10 to 250 mg per kilogram per day), neither boy had symptoms, hypoglycemia, or evidence of hepatic or renal dysfunction, but both had sustained hyperuricemia and hyperuricosuria and increases in the plasma concentration and urinary excretion of magnesium. We conclude that in patients with hereditary fructose intolerance, clinically important chronic fructose intoxication can occur after infancy without causing symptoms of acute fructose intoxication and can be expressed as an apparently isolated, reversible retardation of somatic growth with a continuing disorder of adenine nucleotide metabolism, characterized in part by recurrently increased rates of degradation of adenine nucleotides.

Carbohydrate Metabolism, Inborn Errors↗
PubMed1991

[Metabolic changes in patients with hereditary fructose intolerance. A contribution to the topic of fructose administration for parenteral feeding].

The literature contains a number of reports of death following the intravenous administration of fructose in patients with hereditary fructose intolerance (HFI). The aim of the present study was, therefore, to investigate the metabolic changes occurring during intravenous administration of fructose to patients with HFI, with the aim of identifying metabolic parameters that would permit the early diagnosis of HFI. Also, the deaths reported in the literature were analyzed. In three of our own patients with fruit intolerance known since childhood, and in volunteers with normal metabolism, a one-hour intravenous fructose tolerance test (1.7 g fructose/min) was performed. An analysis was done using the usual enzymatic and chemical methods: blood glucose, fructose, lactic acid, serum uric acid, ammonia, free fatty acids, inorganic phosphate, and serum amino acids (ion exchange chromatography). During fructose infusion, the following metabolic changes were detected: hypoglycemia (20 to 60 mg/dl), increase in blood fructose levels (up to 350 mg/dl), hypophosphatemia (2 to 3 mg/dl), hyperlacticacidemia (up to 60 mg/dl), elevation of plasma ammonia levels (up to 120 mg/dl), increased serum glutamate, and a decrease in serum glutamine, as also hyperuricemia (up to 10 mg/dl). On termination of the fructose infusion, these changes were completely reversible. Analysis of the deaths reported in the literature revealed a known intolerance to fruit or sweets, and that no regular metabolic studies were apparently performed. Although HFI is rare, use should be made of the known advantages of sugar substitutes in post-aggression metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Changes of liver metabolite concentrations in adults with disorders of fructose metabolism after intravenous fructose by 31P magnetic resonance spectroscopy.

A novel 31P magnetic resonance spectroscopy procedure allows the estimation of absolute concentrations of certain phosphorus-containing compounds in liver. We have validated this approach by measuring ATP, phosphomonesters, and inorganic phosphate (Pi) during fasting and after an i.v. fructose bolus in healthy adults and in three adults with disorders of fructose metabolism and by comparing results with known metabolic concentrations measured chemically. During fasting, the ATP concentration averaged 2.7 +/- 0.3 (SD, n = 9) mmol/L, which, after due correction for other nucleoside triphosphates, was 2.1 mmol/L and corresponded well with known concentrations. Fructose-1-phosphate (F-1-P) could not be measured during fasting; its concentration after fructose was calculated from the difference of the phosphomonester signals before (2.9 +/- 0.2 mmol/L) and after fructose. Pi was 1.4 +/- 0.3 mmol/L and represented the one fourth of Pi visible in magnetic resonance spectra. In the three healthy controls after fructose (200 mg/kg, 20% solution, 2.5 min), the fructokinase-mediated increase of F-1-P was rapid, reaching 4.9 mmol/L within 3 min, whereas the uncorrected ATP decreased from 2.7 to 1.8 mmol/L and the Pi from 1.4 to 0.3 mmol/L. The subsequent decrease of F-1-P, mediated by fructaldolase, was accompanied by an overshooting rise of Pi to 2.7 mmol/L. In the patient with essential fructosuria, the concentrations of F-1-P, ATP, and Pi remained unchanged, confirming that fructokinase was indeed inactive. In the patient with hereditary fructose intolerance, initial metabolic changes were the same as in the controls, but baseline concentrations were not yet reestablished after 7 h, indicating weak fructaldolase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1981

Influence of feeding fructose on fructose and glucose absorption in rat jejunum and ileum.

The influence of feeding isocaloric diets containing either 65% of fructose (F 65) on 65% of glucose (G 65) were studied on the uptake of both sugars in segments of rat proximal jejunum and distal ileum. The hexose absorption was compared to that obtained in animals receiving isocaloric amounts of a diet containing 30% of glucose (G 30). Feeding fructose (F 65) for 3 days resulted in a 2.5-fold increase of fructose uptake in the jejunum and a 40% increase in the ileum as compared to group G 30. When fructose (F 65) was administered instead of G 65 the uptake of fructose was enhanced by 75% in the jejunum and 35% in the ileum. Stimulation of glucose absorption in segments of the proximal and distal small intestine by diets F 65 and G 65 was nearly identical as compared to the values of group G 30. The stimulation of the uptake of fructose induced by fructose feeding parallels an adaptive increase in the activity of enzymes involved in fructose metabolism in the mucosa of the small intestine.

Animals↗
PubMed1983

Fructose 1,6-bisphosphatase in rat liver cytosol: interactions between the effects of K+, Zn2+, Mn2+, and fructose 2,6-bisphosphate as measured in a steady-state assay.

Fructose 1,6-bisphosphatase activity was determined in rat liver cytosols using glyceraldehyde 3-phosphate as primary substrate. Fructose 1,6-bisphosphate was formed in situ and steady-state concentrations ranging from 1 to 30 microM were observed depending on the activity of fructose 1,6-bisphosphatase and the concentration of added glyceraldehyde 3-phosphate. The system was free of contaminating low-molecular-weight compounds, divalent cations, and chelators. Under these conditions, fructose 1,6-bisphosphatase was inhibited by K+ (less than or equal to 200 mM). This inhibition was due to a reduction of V and was observed in presence of low (0.4 mM) and high (5 mM) concentrations of Mg2+. In presence of 0.4 mM Mg2+, 1 microM Zn2+ inhibited fructose 1,6-bisphosphatase by 50%; the same effect was obtained with 0.3 microM Zn2+ when the system was supplemented with 100 mM KCl. On the other hand, 0.2 microM Zn2+ enhanced the inhibitory effect of K+ and decreased the concentration of K+ yielding half-maximal inhibition from 175 to 100 mM when measured at 0.4 mM Mg2+. The effect of Zn2+ on the inhibition by K+ could be abolished by Mn2+ (less than 5 microM) or by 5 mM Mg2+. One hundred millimolar K+ enhanced the inhibition of fructose 1,6-bisphosphatase by fructose 2,6-bisphosphate and changed the type of inhibition from mainly competitive to a mixed-type inhibition (increase of Km, decrease of V). Mn2+ (less than 10 microM) reduced the effect of fructose 2,6-bisphosphate, especially in the presence of K+. It is proposed that K+ and Mn2+ may play a role in the regulation of gluconeogenesis.

Animals↗
PubMed1980

Studies on the regulation of chloroplast fructose-1,6-bisphosphatase. Activation by fructose 1,6-bisphosphate.

Chloroplast fructose-1,6-bisphosphatase (D-fructose 1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) isolated from spinach leaves, was activated by preincubation with fructose 1,6-bisphosphate. The rate of activation was slower than the rate of catalysis, and dependent upon the temperature and the concentration of fructose 1,6-bisphosphate. The addition of other sugar diphosphates, sugar monophosphates or intermediates of the reductive pentose phosphate cycle neither replaced fructose 1,6-bisphosphate nor modified the activation process. Upon activation with the effector the enzyme was less sensitive to trypsin digestion and insensitive to mercurials. The activity of chloroplast fructose-1,6-bisphosphatase, preincubated with fructose 1,6-bisphosphate, returned to its basal activity after the concentration of the effector was lowered in the preincubation mixture. The results provide evidence that fructose-1,6-bisphosphatase resembles other regulatory enzymes involved in photosynthetic CO2 assimilation in its activation by chloroplast metabolites.

Chloroplasts↗
PubMed2004

Isotopic discrimination between D-[1-(13)C]fructose and D-[2-(13)C]fructose in rat liver cells.

When liver cells from either normal or hereditarily diabetic rats are exposed to (13)C-enriched D-fructose (10 mM) and unlabelled D-glucose (also 10 mM) in the presence of D(2)O, the output of (13)C-enriched D-glucose generated from D-[1-(13)C]fructose is significantly lower than that from D-[2-(13)C]fructose. This coincides with a higher generation of (13)C-enriched L-lactate and L-alanine from D-[1-(13)C]fructose, as compared to D-[2-(13)C]fructose. In absolute terms, the mean paired difference in the output of (13)C-enriched D-glucose generated from D-[1-(13)C]fructose versus D-[2-(13)C]fructose is not significantly different from the mean paired difference in the production of (13)C-enriched L-lactate and L-alanine from the same precursors, with an overall mean value of 7.01 +/- 1.59 micromol (n = 8; P < 0.005). It is proposed that these findings indicate isotopic discrimination at the phosphoglucoisomerase level between (12)C and (13)C for the carbon atom in position 1 (as compared to that in position 2) of D-fructose 6-phosphate.

Alanine↗
PubMed2006

Expression of fructose sensitive glucose transporter in the brains of fructose-fed rats.

Glucose transporters play a critical role in mammalian brain energy metabolism because glucose is the principal brain energy source and these transporters promote glucose movement into neural cells. When glucose is unavailable, fructose can serve as an alternative energy source. Using real-time polymerase chain reaction and actin as a reference mRNA, we investigated the impact of fructose feeding on rat brain and other tissue mRNA expression of glucose transporter 5 which has high affinity for fructose. Brain mRNA levels of glucose transporter 5 increased 1.5-fold in 35-day old rats after 7 days of fructose feeding compared with controls, whereas it increased 2.5-fold in jejunum. Semi-quantitative analysis of protein expression by immunofluorescence of glucose transporter 5 in rat hippocampi indicated a 2.4-fold increase. We demonstrated the specificity of fructose feeding on glucose transporter 5 expression by showing that the expression of the neuronal glucose transporter 3 and insulin-regulated glucose transporter 4 were unaffected. In addition, the expression of glucose transporter 5 increased in fructose fed older adult rats (8-months and 12-months old) when compared with controls. These results suggest that short-term fructose feeding increases the expression of glucose transporter 5 in both young and aging adult rats. Increased brain expression of glucose transporter 5 is likely to be important in the role of fructose as an alternative energy source.

Age Factors↗
PubMed2000

Fructose utilization and pathogenicity of Spiroplasma citri: characterization of the fructose operon.

Transposon Tn4001 mutagenesis of Spiroplasma citri wild-type (wt) strain GII-3 led to the isolation and characterization of non-phytopathogenic mutant GMT 553. In this mutant, transposon Tn4001 is inserted within the first gene of the fructose operon. This operon comprises three genes. The first gene (fruR) codes for a putative transcriptional regulator protein belonging to the deoxyribonucleoside repressor (DeoR) family. Sequence similarities and functional complementation of mutant GMT 553 with different combinations of the wt genes of the fructose operon showed that the second gene (fruA) codes for the permease of the phosphoenolpyruvate:fructose phosphotransferase system (fructose PTS), and the third, fruK, for the 1-phosphofructokinase (1-PFK). Transcription of the fructose operon in wt strain GII-3 resulted in two messenger RNAs, one of 2.8kb and one of 3.8kb. Insertion of Tn4001 in the genome of mutant GMT 553 abolished transcription of the fructose operon, and resulted in the inability of this mutant to use fructose. Functional complementation experiments demonstrated that fructose utilization was restored with fruR-fruA-fruK, fruA-fruK or fruA only, but not with fruR or fruR-fruA. This is the first time that an operon for sugar utilization has been functionally characterized in the mollicutes.

Amino Acid Sequence↗
PubMed1986

Regulation of rabbit liver fructose-1,6-bisphosphatase by metals, nucleotides, and fructose 2,6-bisphosphate as determined from fluorescence studies.

The fluorescent nucleotide analogue formycin 5'-monophosphate (FMP) inhibits rabbit liver fructose-1,6-bisphosphatase (I50 = 17 microM, Hill coefficient = 1.2), as does the natural regulator AMP (I50 = 13 microM, Hill coefficient = 2.3), but exhibits little or no cooperativity of inhibition. Binding of FMP to fructose-1,6-bisphosphatase can be monitored by the increased fluorescence emission intensity (a 2.7-fold enhancement) or the increased fluorescence polarization of the probe. A single dissociation constant for FMP binding of 6.6 microM (4 sites per tetramer) was determined by monitoring fluorescence intensity. AMP displaces FMP from the enzyme as evidenced by a decrease in FMP fluorescence and polarization. The substrates, fructose 6-phosphate and fructose 1,6-bisphosphate, and inhibitors, methyl alpha-D-fructofuranoside 1,6-bisphosphate and fructose 2,6-bisphosphate, all increase the maximal fluorescence of enzyme-bound FMP but have little or no effect on FMP binding. Weak metal binding sites on rabbit liver fructose-1,6-bisphosphatase have been detected by the effect of Zn2+, Mn2+, and Mg2+ in displacing FMP from the enzyme. This is observed as a decrease in FMP fluorescence intensity and polarization in the presence of enzyme as a function of divalent cation concentration. The order of binding by divalent cations is Zn2+ = Mn2+ greater than Mg2+, and the Kd for Mn2+ displacement of FMP is 91 microM. Methyl alpha-D-fructofuranoside 1,6-bisphosphate, as well as fructose 6-phosphate and inorganic phosphate, enhances metal-mediated FMP displacement from rabbit liver fructose-1,6-bisphosphatase.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Monophosphate↗
PubMed1974

Requirement for a functional respiration-coupled D-fructose transport system for induction of phosphoenolypyruvate:D-fructose phosphotransferase activity.

Previous studies have shown that Arthrobacter pyridinolis can transport D-fructose or L-rhamnose using either a phosphoenolpyruvate:hexose phosphotransferase (phosphoenolpyruvate:protein phosphotransferase, EC 2.7.3.9) system or a respiration-coupled transport system which requires the presence of exogenous L-malate. A mutant, AP4374, which is deficient in the D-fructose-specific component of the respiration-coupled system can grow on L-rhamnose using the phosphotransferase system, but cannot grow on D-fructose at all. AP4374 fails to produce the inducible D-fructose-specific phosphotransferase components (enzyme II and factor III) when grown in the presence of D-fructose. These results indicate a requirement for a functional respiration-coupled transport system for induction of the phosphotransferase system. The results further suggest that sufficient free D-fructose (or D-fructose 6-phosphate derived from it) must be present inside the cell in order for induction of the phosphotransferase system to occur. The entry of sufficient fructose to cause induction of the phosphotransferase system cannot occur by facilitated diffusion in the absence of energy coupling.

Arthrobacter↗
PubMed1984

Response of plasma glucose, fructose and insulin to dietary glucose and fructose in the lactating sow.

Twenty-two Hampshire-Yorkshire X Large White sows of second and third parity were allotted randomly to one of three dietary treatments. Five sows were fed 6.0 kg/day of a corn-soybean meal lactation diet (control diet). Twelve sows were fed the control diet in which 24% of the composition was supplied by corn syrup containing 72% fructose on a dry matter basis (fructose diet) and five sows were fed the control diet in which 24% of the composition was supplied by powdered dextrose (glucose diet). All diets were fed from days 1 through 21 of lactation. Blood was collected from all sows immediately prior to feeding and hourly for 6 hours postprandial via jugular vein cannulae following a single feeding on seven separate but nonconsecutive days during the 21-day period. Fructose was absorbed from the digestive tract of sows as evidenced by elevated (P less than 0.01) conventions of fructose in plasma. Sows fed the fructose diet also had higher (P less than 0.01) plasma glucose concentrations than did those fed the glucose and control diets. The concomitant elevated glucose concentration following ingestion of the fructose diet was not associated (P greater than 0.10) with increased insulin concentration. Fructose in plasma was associated with a slight but significant increase in insulin although the mean concentration of insulin in plasma was only one-third that measured in sows fed the glucose and control diets. These data suggest that fructose in vivo has a glucose-sparing effect presumably mediated through a physiological mechanism that lowers insulin concentration.

Animals↗
PubMed1993

Fructose utilization during exercise in men: rapid conversion of ingested fructose to circulating glucose.

The aim of the present study was to compare the metabolic fate of repeated doses of fructose or glucose ingested every 30 min during long-duration moderate-intensity exercise in men. Healthy volunteers exercised for 3 h on a treadmill at 45% of their maximal oxygen consumption rate. "Naturally labeled" [13C]glucose or [13C]fructose was given orally at 25-g doses every 30 min (total feeding: 150 g; n = 6 in each group). Substrate utilization was evaluated by indirect calorimetry, and exogenous sugar oxidation was measured by isotope ratio mass spectrometry on expired CO2. Results were corrected for baseline drift in 13C/12C ratio in expired air due to exercise alone. Fructose conversion to plasma glucose was measured combining gas chromatography and isotope ratio mass spectrometry. Most of the ingested glucose was oxidized: 81 +/- 4 vs. 57 +/- 2 g/3 h for fructose (2P < 0.005). Exogenous glucose covered 20.8 +/- 1.4% of the total energy need (+/- 6.7 MJ) compared with 14.0 +/- 0.6% for fructose (2P < 0.005). The contribution of total carbohydrates was significantly higher and that of lipids significantly lower with glucose than with fructose. The blood glucose response was similar in both protocols. From 90 to 180 min, 55-60% of circulating glucose was derived from ingested fructose. In conclusion, when ingested repeatedly during moderate-intensity prolonged exercise, fructose is metabolically less available than glucose, despite a high rate of conversion to circulating glucose.

Adult↗
PubMedDate not supplied

The effects of sucrose, fructose, and high-fructose corn syrup meals on plasma glucose and insulin in non-insulin-dependent diabetic subjects.

We have previously shown that fructose and sorbitol given with a standard meal cause less increment in plasma glucose than sucrose and high fructose corn syrup (HFCS) in patients with NIDDM. However, there was no direct comparison of sucrose with HFCS. Sixteen men and one woman aged 54-67) with NIDDM were given either 35 g sucrose, 35 g fructose, or 43.75 g HFCS containing 35 g carbohydrate as part of a 400-calorie test meal. Blood samples were obtained at frequent intervals up to 3 h and were analyzed for glucose and insulin. As compared with a fructose meal, the mean increment in plasma glucose (delta PG) after a sucrose meal was significantly higher at 45 min and after an HFCS meal it was significantly higher at 30 and 45 min, but sucrose and HFCS meals did not differ. When delta PGs were compared in nine patients with basal PG greater than 140 mg/dl and in eight patients with basal PG less than 140 mg/dl, differences in delta PG after sucrose and HFCS versus fructose meals became more significant but still did not differ from each other. The integrated total areas under the delta PG curves after sucrose, HFCS, and fructose meals were not statistically different. However, the areas under the curves up to 90 min after sucrose and HFCS meals, which did not differ, were greater than the fructose meal. The mean delta IRI after sucrose meals was markedly elevated at 45, 60, and 75 min (P less than 0.05) and after HFCS meals at 45 min as compared with fructose meals.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1976

[The fructose induced "glycogenosis". II. Histochemical studies of glycogen metabolism in rat liver after fructose overload and similar diets (author's transl)].

INTRODUCTION: Feeding of fructose for 7 days has been morphometrically shown to induce a SER-reduction and an accumulation of glycogen in rat liver cells. This hypothetical model "glycogenosis" is investigated with histochemical methods. MATERIAL AND METHODS: Rats are given a solution of 60% fructose in water as only nutritional source. Controls are given a solution of 60% glucose in water, an isocaloric Altromin-R-standard diet and an Altromin-R-standard diet ad libitum. Reversion of fructose induced metabolic changes is investigated by a 7 days fructose diet followed by an 1-4 days Altromin-R-standard diet ad libitum. Glycogen and glycogen metabolizing enzymes are demonstrated after a 7 days diet and in the course of an 1-7 days fructose diet. RESULTS AND DISCUSSION: Feeding of fructose leads to a high glycogen content, combined with a high activity of glycogen-phosphorylase and glucose-6-phosphatase in the liver parenchyma. Glycogen-synthetase activity increases during the first 4 days and then it drops to a low level. A pathological alteration of liver cell metabolism seems to be improbable, for all fructose induced changes are reversibel after 2 days of Altromin-R-standard diet. Glucose-6-phosphatase, as a marker-enzyme of the smooth endoplasmatic reticulum, is discussed to become activated by disruption of SER membranes due to fructose.

Acid Phosphatase↗
PubMed1996

Islet fructose 6-phosphate, 2-kinase:fructose 2,6-bisphosphatase: isozymic form, expression, and characterization.

Polymerase chain reaction analysis of the mRNA isolated from rat islets demonstrated that the major isozyme of Fructose 6-P,2-kinase:Fructose 2,6-bisphosphatase was the heart type enzyme, and that the liver type enzyme was not detectable. The islet enzyme was expressed in Escherichia coli and purified to homogeneity. The islet enzyme showed the highest Fructose 6-P,2-kinase activity (478 milliunits/mg) compared to the other isozymes and Fructose 2,6-Pase activity (39 milliunits/mg). Fructose 6-P,2-kinase showed KmF6P = 17 microM, which is within the range of in vivo Fru 6-P concentrations in islets. 6-P-Gluconate was a potent inhibitor of Fructose 2,6-Pase. The data suggest that Fructose 6-P,2-kinase activity of the bifunctional enzyme was high and Fructose 2,6-Pase activity was inhibited under physiological variations of blood glucose concentration.

Animals↗