Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Fructokinases”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed1984

Fructose utilization by lung.

We have examined the role of fructose as a substrate for the mammalian lung. Isolated and ventilated rat lungs were perfused for 2 h in the presence of either [U-14C]- or [5-3H]fructose. Fructose utilization, 3H2O production, and lactate and pyruvate production were measured. Insulin had no effect on the production of radiolabeled lactate. The 14C label from [U-14C]fructose was incorporated into the neutral lipids, phospholipids, fatty acid moiety, and deacylated fraction of lung. The apparent Km and maximum velocity of enzyme reaction for fructose utilization were 0.5 mM and 75 nmol X h-1 X g dry wt-1, respectively. Recovery of fructose 1-phosphate and fructose 1,6-diphosphate after perfusion with fructose, as well as detection of fructokinase, aldolase, and triokinase activities in the lung homogenates, suggested that fructose had been metabolized via phosphorylation through fructose 1-phosphate. Activities of fructose-metabolizing enzymes were not altered by the induction of diabetes, hypophysectomy, or starvation. These results suggest that mammalian lungs may utilize fructose to synthesize fatty acids, which in turn are used for phospholipid biosynthesis. The utilization of fructose by lung does not seem to be affected by nutritional or hormonal conditions.

Animals↗
PubMed1995

A new enzymatic method for the determination of inulin.

A new enzymatic method for the determination of inulin in plasma and urine, using inulase (EC 3.2.1.7), fructokinase (EC 2.7.1.4), phosphoglucoisomerase (EC 5.3.1.9) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49) is described. The assay is based on the hydrolysis of inulin or Inutest (INutest which is the injectable form of inulin), by inulase and the determination of fructose released. The assay was linear up to 2 g/L of Inutest. The within-batch and between batch coefficients of variation were 2.3% and 2.2%, respectively. Recovery of added Inutest from plasma and urine was 98-102%. There was no interference from glucose (27.7 mmol/L), fructose (1.7 mmol/L) or mannose (1.7 mmol/L). When inulin clearance (using this method) and thiosulphate clearance were compared in 37 patients the inulin clearance was 9.3 mL/min (12%) lower than the thiosulphate clearance. We conclude that this enzymatic method is a simple and specific method.

Anthracenes↗
PubMed2003

Properties of normal and mutant recombinant human ketohexokinases and implications for the pathogenesis of essential fructosuria.

Alternative splicing of the ketohexokinase (fructokinase) gene generates a "central" predominantly hepatic isoform (ketohexokinase-C) and a more widely distributed ketohexokinase-A. Only the abundant hepatic isoform is known to possess activity, and no function is defined for the lower levels of ketohexokinase-A in peripheral tissues. Hepatic ketohexokinase deficiency causes the benign disorder essential fructosuria. The molecular basis of this has been defined in one family (compound heterozygosity for mutations Gly40Arg and Ala43Thr). Here we show that both ketohexokinase isoforms are indeed active. Ketohexokinase-A has much poorer substrate affinity than ketohexokinase-C for fructose but is considerably more thermostable. The Gly40Arg mutation seems null, rendering both ketohexokinase-A and ketohexokinase-C inactive and largely insoluble. The Ala43Thr mutant retains activity, but this mutation decreases the thermal stability of both ketohexokinase-A and ketohexokinase-C. At physiologic temperature, this results in significant loss of ketohexokinase-C activity but not of ketohexokinase-A. Affected individuals who carry both mutations therefore probably have a selective deficiency of hepatic ketohexokinase, with peripheral ketohexokinase-A being preserved. These findings raise the possibility that ketohexokinase-A serves an unknown physiologic function that remains intact in essential fructosuria. Further mutation analysis in this rare disorder could illuminate the question of whether ketohexokinase-A activity is, unlike that of ketohexokinase-C, physiologically indispensable.

Alternative Splicing↗
PubMed1980

Characterization of Leishmania spp. by isozyme electrophoresis.

In this study, isozyme patterns for 14 different enzymes were compared for culture strains of Leishmania braziliensis, L. hertigi, L. mexicana, L. donovani, L. tropica, and L. adleri. The isozyme separation was made by means of cellulose acetate electrophoresis. Each of the species had distinct isozyme patterns for aspartate aminotransferase, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and fructokinase. For other enzymes, two or more species had identically migrating bands; however, by using combinations of the other 10 enzymes it was possible to separate any one of the six species. In addition to these interspecific differences the Panama strains of L. braziliensis had two different malic dehydrogenase isozyme patterns; therefore, they fell into two distinct groups. These strains otherwise had identical isozyme patterns.

Animals↗
PubMed2000

Analysis of a catabolic operon for sucrose transport and metabolism in Clostridium acetobutylicum ATCC 824.

The utilization of sucrose by Clostridium acetobutylicum ATCC 824 was investigated. Sucrose was found to be transported via a phosphoenol-pyruvate (PEP)-dependent phosphotransferase system (PTS) and a metabolic pathway identical to that previously identified in C. beijerinckii, was established. The genes encoding the proteins of this pathway were identified from the C. acetobutylicum genome sequence, in the order scrAKB encoding Enzyme II of the sucrose PTS, fructokinase and sucrose 6-phosphate hydrolase respectively. While the pathway for sucrose metabolism is conserved between C. acetobutylicum and C. beijerinckii, the operons show considerable differences in organization and regulatory elements. The C. acetobutylicum scr operon contains the elements of an antiterminator-mediated regulation mechanism, typical of the BgIG family of regulators. The scrT gene, located upstream of scrA encodes an antiterminator that is preceded by a transcription terminator, which is overlapped by a classical ribonucleic antiterminator (RAT) sequence. We also propose the existence of a new variant RAT-like sequence which overlaps a terminator between scrT and the downstream structural genes.

Amino Acid Sequence↗
PubMed1985

Nutritional and hormonal control of glucose and fructose utilization by lung.

Whereas glucose is a major substrate for pulmonary lipid synthesis, fructose has also been suggested as a potential substrate. In vivo pulmonary fatty acid synthesis is depressed in hormonally deprived conditions, such as diabetes, and this can be modified by fructose feeding, but not by glucose feeding. In this study the glucose and fructose utilizations were compared in normal, diabetic and fasting states using isolated perfused rat lungs. When (U-14C)- or (5-3H)-glucose was used as substrate, glucose utilization by lung was reduced by 50% in both the fasting and diabetic animals compared to the normal controls. Using (U-14C)-glucose as substrate, the incorporation of (14C)-label in various metabolites of glucose was significantly depressed. For example, this reduction was 50% in lactate, pyruvate and CO2, 15% in ethanol-insoluble fraction, 65% in neutral lipids, 75% in phospholipids, 80% in fatty acid moiety, 40% in deacylated fraction and 10% in the polysaccharide fractions. Refeeding the fasted animals or insulin treatment to the diabetic animals restored these depressed (14C)-recoveries to the normal levels. Fructose utilization was less than 10% of glucose utilization, but remained unaffected by fasting and diabetic states. In addition, pulmonary hexokinase enzyme activity was lowered significantly in fasting and diabetic animals, whereas fructokinase enzyme activity was not altered. Despite the low rate of fructose utilization, these results suggest that fructose may serve as an alternative substrate for pulmonary phospholipid synthesis when glucose utilization is significantly depressed.

Animals↗
PubMed1981

[Effect of high-dose parenteral fructose, glucose and mannitol on the rat kidney].

As previously observed after infusions of glycerol, fructose infusions with rates above the average maximal turnover capacity (3.5 g X kg-1 X h-1) result in damage of the kidneys as shown by a decrease of the total activity of glycerokinase and fructokinase and excretion of glycerokinase in the urine. Beginning alterations of the kidneys are dependent on time and dose become evident by a depletion of protein per gram fresh weight. In the beginning of the changes the total activity of enzymes in the kidneys remaining constant. Interrelations between the observed kidney alterations, turnover capacity, substrate concentrations in the blood, and the rate of renal excretion are discussed with regard to the results after infusions of glucose and mannitol. For infusion therapy it can be deduced, that dosage in borderline cases should be determined by the blood level of the substrate rather than by body weight, if undesirable effects are to be avoided.

Animals↗
PubMed1989

A 31P NMR study of the GI tract: effect of fructose loading and measurement of transverse relaxation times.

The effect of fructose loading on high-energy phosphates in the jejunum, ileum, and large intestine of rats was studied using 31P NMR. Following fructose loading, an increase in the intensity of the PME resonance was observed in the jejunum, indicating an accumulation of fructose-1-phosphate. There were no significant changes in ATP or Pi. This demonstrates that the activity of fructokinase in the jejunum can be monitored by 31P NMR. Fructose loading had no detectable effect on metabolite levels in the ileum and large intestine. Resolution of intestinal spectra was poor due to unusually large linewidths and the presence of broad underlying signals. To study the mechanism of line broadening, the T2's of the phosphorus resonances were measured using a solenoidal coil. The T2's of the ATP, Pi, PME, and PCr resonances were much longer than the T2's, suggesting that the linewidths of these resonances are primarily due to susceptibility gradients and/or compartmentation of metabolites. Other signals, particularly in the PDE region, were homogeneously broadened and had very short T2's. Spin echoes obtained with evolution times of 1 to 4 ms suppressed these broad components, with little loss of intensity in the inhomogeneously broadened resonances; as a result, resolution was improved.

Animals↗
PubMed2003

Proteome analysis of male gametophyte development in rice anthers.

We used proteomic analysis to investigate the changing patterns of protein synthesis during pollen development in anthers from rice plants grown under strictly controlled growth conditions. Cytological analysis and external growth measurements such as anther length, auricle distances and days before flowering were used to determine pollen developmental stages. This allowed the collection of synchronous anther materials representing six discrete pollen developmental stages. Proteins were extracted from the anther samples and separated by two-dimensional gel electrophoresis to produce proteome maps. The anther proteome maps of different developmental stages were compared and 150 protein spots, which were changed consistently during development, were analysed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry to produce peptide mass fingerprint (PMF) data. Database searches using these PMF data revealed the identities of 40 of the protein spots analyzed. These 40 proteins represent 33 unique gene products. Four protein spots that could not be identified by PMF analysis were analysed by N-terminal microsequencing. Multiple charge-isoforms of vacuolar acid invertase, fructokinase, beta-expansin and profilin were identified. These proteins are closely associated with sugar metabolism, cell elongation and cell expansion, all of which are cell activities that are essential to pollen germination. The existence of multiple isoforms of the same proteins suggests that during the process of pollen development some kind of post-translational modification of these proteins occurs.

Amino Acid Sequence↗
PubMed1999

Metabolic and secretory response to D-fructose in pancreatic islets from adult rats injected with streptozotocin during the neonatal period.

The metabolic and secretory responses to D-glucose and/or D-fructose were measured in pancreatic islets prepared from either control rats or animals that had been injected with streptozotocin during the neonatal period (STZ rats). The STZ rats displayed higher plasma D-glucose concentrations, but lower plasma insulin concentrations, islet insulin content, as well as basal and nutrient-stimulated insulin release. This coincided with lower rates of D-[U-(14)C]hexose oxidation and D-[5-(3)H]hexose utilization. In both control and STZ rats, D-fructose failed to affect significantly the metabolism of d-glucose, while the aldohexose increased the ratio between D-[U-(14)C]fructose oxidation and D-[5-(3)H]fructose conversion to (3)HOH. Such a ratio was higher than that found with radioactive D-glucose in islets exposed to both hexoses, whether in control or STZ rats, indicating a far-from-negligible contribution of fructokinase to the phosphorylation of D-fructose. Despite these analogies between both the respective fate of D-glucose and D-fructose and the reciprocal metabolic effects of the two hexoses in islets from control and STZ rats, the secretory response to the ketohexose in islets from STZ rats was preferentially suppressed, relative to that evoked by the aldohexose. This gives support to the idea that the insulinotropic action of D-fructose may not be entirely accounted for by its nutritional value in islet cells.

Animals↗
PubMed2002

Metabolism of D-[1-(13)C]fructose, D-[2-(13)C]fructose, and D-[6-(13)C]fructose in rat hepatocytes incubated in the presence of H(2)O or D(2)O.

Isolated hepatocytes from fed rats were exposed for 120 min to D-[1-(13)C]fructose, D-[2-(13)C]fructose, or D-[6-(13)C]fructose in the presence of H(2)O or D(2)O. The identification and quantification of (13)C-enriched metabolites (D-glucose, L-lactate) in the incubation medium and the measurement of their deuterated isotopomers indicated that the ketohexose was phosphorylated predominantly at the intervention of fructokinase and that the majority of the D-glyceraldehyde molecules generated from d-fructose 1-phosphate were further metabolized, e.g., after phosphorylation to D-glyceraldehyde 3-phosphate. It is proposed that the present procedure may help to further characterize the regulation of D-fructose metabolism in both hepatocytes and other cell types.

Animals↗
PubMed1975

Enzymes of D-fructose catabolism in species of Beneckea and Photobacterium.

Cell-free extracts of strains representative of the genera Beneckea and Photobacterium catalyzed a P-enolpyruvate dependent phosphorylation of D-fructose. The resulting product, fructose-1-P, was converted to fructose-1,6-P2 by 1-P-fructokinase. Both activities were inducible, being present in D-fructose-grown cells and reduced or absent in D-gluconate-(or succinate-) grown cells.

Adenosine Triphosphate↗
PubMed1977

Different degradation pathways for glucose and fructose in Rhodopseudomonas capsulata.

In Rhodopseudomonas capsulata the enzymes of the Entner-Doudoroff pathway and the Embden-Meyerhof pathway have been examined. Fructose-grown cells contained inducible activities of phosphoenolpyruvate-fructosephospho-transferase and 1-phosphofructokinase and only low levels of fructokinase and 6-phosphofructokinase. Although fructose-grown cells contained, in addition, all the enzymes of the Entner-Doudoroff pathway together with fructose-1,6-diphosphatase and phosphoglucose isomerase, the Entner-Doudoroff pathway was not operative in fructose catabolism and served only the degradation of glucose. The functional separation of glucose and fructose catabolism via the Entner-Doudoroff and a modified Embden-Meyerhof pathway, respectively, was confirmed by different approaches: 1. Radiorespirometric experiments with glucose and fructose labelled in positions 1, 2, 3, 3+4 and 6 have been carried out. The pattern of 14CO2-evolution from position-labelled glucose was characteristic for the Entner-Doudoroff pathway, that from position-labelled fructose for the Embden-Meyerhof pathway. 2. In the presence of arsenite up to 50% of glucose- and fructose-carbon was excreted as pyruvate. Using 1-14C-glucose, 86% of the pyruvate was labelled in the carboxyl group, whereas using 1-14C-fructose only 19% of the pyruvate was labelled in the carboxyl group. 3. A glucose-6-phosphate dehydrogenase-deficient mutant was isolated which lacked a functional Entner-Doudoroff pathway but which was unaltered in its ability to grow on fructose.

Fructose↗
PubMed2005

Sugar signalling and gene expression in relation to carbohydrate metabolism under abiotic stresses in plants.

Sucrose is required for plant growth and development. The sugar status of plant cells is sensed by sensor proteins. The signal generated by signal transduction cascades, which could involve mitogen-activated protein kinases, protein phosphatases, Ca 2+ and calmodulins, results in appropriate gene expression. A variety of genes are either induced or repressed depending upon the status of soluble sugars. Abiotic stresses to plants result in major alterations in sugar status and hence affect the expression of various genes by down- and up-regulating their expression. Hexokinase-dependent and hexokinase-independent pathways are involved in sugar sensing. Sucrose also acts as a signal molecule as it affects the activity of a proton-sucrose symporter. The sucrose trans-porter acts as a sucrose sensor and is involved in phloem loading. Fructokinase may represent an additional sensor that bypasses hexokinase phosphorylation especially when sucrose synthase is dominant. Mutants isolated on the basis of response of germination and seedling growth to sugars and reporter-based screening protocols are being used to study the response of altered sugar status on gene expression. Common cis-acting elements in sugar signalling pathways have been identified. Transgenic plants with elevated levels of sugars/sugar alcohols like fructans, raffinose series oligosaccharides, trehalose and mannitol are tolerant to different stresses but have usually impaired growth. Efforts need to be made to have transgenic plants in which abiotic stress responsive genes are expressed only at the time of adverse environmental conditions instead of being constitutively synthesized.

Carbohydrate Metabolism↗
PubMed2006

Biochemical study of the anti-diabetic action of the Egyptian plants fenugreek and balanites.

Fenugreek and Balanites are two plants commonly used in Egyptian folk medicine as hypoglycemic agents. In the present study, the effects of 21 days oral administration of Fenugreek seed and Balanites fruit extracts (1.5 g/kg bw) on the liver and kidney glycogen content and on some key liver enzymes of carbohydrate metabolism in STZ-diabetic rats were studied. In addition, the effects of these two plant extracts on the intestinal alpha-amylase activity in vitro and starch digestion and absorption in vivo were also examined. Results indicated that single injection of STZ (50 mg/kg bw) caused 5-folds increase in the blood glucose level, 80% reduction in serum insulin level, 58% decrease in liver glycogen and 7-folds increase in kidney glycogen content as compared to the normal levels. The activity of glucose-6-phosphatase was markedly increased, whereas, the activities of both glucose-6-phosphate dehydrogenase and phospho-fructokinase were significantly decreased in the diabetic rat liver. Administration of Fenugreek extract to STZ-diabetic rats reduced blood glucose level by 58%, restored liver glycogen content and significantly decreased kidney glycogen as well as liver glucose-6-phosphatase activity. Meanwhile, Balanites extract reduced blood glucose level by 24% and significantly decreased liver glucose-6-phosphatase activity in diabetic rats. On the other hand, our results demonstrated that both the Fenugreek and Balanites extracts were able to in vitro inhibit alpha-amylase activity in dose-dependent manner. Fenugreek was more potent inhibitor than Balanites. This inhibition was reversed by increasing substrate concentration in a pattern which complies well with the effect of competitive inhibitors. Furthermore, this in vitro inhibition was confirmed by in vivo suppression of starch digestion and absorption induced by both plant extracts in normal rats. These findings suggest that the hypoglycemic effect of Fenugreek and Balanites is mediated through insulinomimetic effect as well as inhibition of intestinal alpha-amylase activity.

Animals↗
PubMed2005

Comparison of expression of glucokinase gene and activities of enzymes related to glucose metabolism in livers between dog and cat.

Plasma glucose and immunoreactive insulin (IRI) concentrations and activities of enzymes related to glucose metabolism in livers were measured in dogs and cats. Nucleotide sequences of the conserved region of glucokinase (GK) cDNA that contained ATP- and glucose-binding domains were determined in canine liver and feline pancreas for design of the species-specific oligonucleotide primers for reverse transcription-polymerase chain reaction (RT-PCR) analysis. There were no significant differences in plasma glucose and IRI concentrations between dogs and cats. In feline liver, although GK activities were not detected, activities of hexokinase, fructokinase, pyruvate kinase, glucose-6-phosphate dehydrogenase, fructose-1,6-bisphosphatase and glucose-6-phosphatase were significantly higher than those in canine liver. The partial sequences of canine liver GK and feline pancreas GK cDNA were respectively 88% and 89% identical with the rat liver GK cDNA. Expression of GK gene was observed in canine liver and pancreas and feline pancreas with RT-PCR using species specific primers based on the cDNA sequences.

Animals↗
PubMed1984

Effect of aging on changes in substrate and effector levels of rat-liver glycolytic and lipogenic enzymes during induction.

When 1-, 2- and 9-month-old rats adapted to a stock diet were fed a fat-free/high-sucrose diet, the changes in the substrate and effector levels of glycolytic and lipogenic enzymes in liver, and the effects of aging on the changes were investigated. By the sucrose diet feeding, the activities of phosphofructokinase, pyruvate kinase and fructokinase were increased, whereas hexokinase activity was markedly decreased. The fructose 1-phosphate levels were significantly increased in the liver, while conversely, the glucose 6-phosphate and fructose 6-phosphate levels were decreased. As a result of sucrose diet feeding, the changed enzyme activities would appear to be consistent with the metabolic pathway for fructose being predominant over that for glucose. Consequently, the concentrations of acetyl-CoA, citrate and malate were increased and would in turn appear to favour an increase in lipogenesis. The changes in the substrate and effector levels of lipogenic enzymes were reduced with aging, as were those in the enzyme activities. However, the changes in enzyme activities and metabolite levels of glycolysis were not much affected with aging.

Acetyl-CoA Carboxylase↗
PubMed1983

Metabolism and bound water in overwintering insects.

The freezing-tolerant gall fly larva, Eurosta solidaginis, provides an excellent model system for the study of metabolic adaptation and metabolic control for low-temperature survival during overwintering. Low-temperature acclimation of the larvae results in dramatic alterations in metabolic flux producing a sequential synthesis of two cryoprotectants, glycerol at warmer temperatures followed by sorbitol when larvae are exposed to 5 degrees C. Regulation of metabolism in the larvae appears to exploit temperature change, temperature effects on enzyme kinetics, and temperature/modulator interactions with enzymes producing the alterations in metabolic flux leading to differential polyol synthesis. For instance, temperature/modulator effects on phospho-fructokinase appear to be the major factor halting carbon flow into glycerol synthesis at low temperatures and diverting flux instead into the pathway of sorbitol synthesis. Alterations in the cellular content of bound water and the metabolic pools of free versus bound soluble metabolites may also have important regulatory consequences for low-temperature metabolism. Bound water content of the larvae increases with low-temperature acclimation and is attributable to changes in water binding by both low-molecular-weight (polyols) and high-molecular-weight (proteins, glycogen) subcellular components. A restrictive effect of high bound water content may be one factor causing the strong depression of metabolic activity seen in the larvae as a result of extracellular freezing. In addition, bound water may have a more subtle effect in determining the relative pool sizes of bound versus free metabolites in the cell. 31P-NMR studies of whole larvae show that the content of free phosphorylated intermediates in the cell diminishes with decreasing temperatures despite a measured constancy in the total pool size of these intermediates. An increase in the content of bound metabolites with low temperature may restrict metabolism by limiting the availability of substrates and effectors of enzyme reactions.

Adaptation, Biological↗