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 271 records · Page 15Linked to original sources
PubMed2003

Heterologous expression of a ketohexokinase in potato plants leads to inhibited rates of photosynthesis, severe growth retardation and abnormal leaf development.

In the present paper we investigated the effect of heterologous expression of a rat liver ketohexokinase in potato (Solanum tuberosum L.) plants with the aim of investigating the role of fructose 1-phosphate in plant metabolism. Plants were generated that contained appreciable activity of ketohexokinase but did not accumulate fructose 1-phosphate. They were, however, characterised by a severe growth retardation and abnormal leaf development. Studies of (14)CO(2) assimilation and metabolism, and of the levels of photosynthetic pigments, revealed that these lines exhibited restricted photosynthesis. Despite this fact, the levels of starch and soluble sugars remained relatively constant. Analysis of intermediates of starch and sucrose biosynthesis revealed large increases in the triose phosphate and fructose 1,6-bisphosphate pools but relatively unaltered levels of inorganic phosphate and 3-phosphoglycerate, and these lines were also characterised by an accumulation of glyceraldehyde. The transformants neither displayed consistent changes in the activities of Calvin cycle enzymes nor in enzymes of sucrose synthesis but displayed a metabolic profile partially reminiscent of that brought about by end-product limitation, but most likely caused by an inhibition of photosynthesis brought about by the accumulation of glyceraldehyde. Analysis of the metabolite contents in lamina and vein fractions of the leaf, and of the enzymes of carbohydrate oxidation indicate that the phloem-enriched veins of ketohexokinase-expressing leaves tend toward hypoxia and indicate a problem of phloem transport.

Animals↗
PubMed2006

Assessing the potential for unintended effects in genetically modified potatoes perturbed in metabolic and developmental processes. Targeted analysis of key nutrients and anti-nutrients.

Targeted compositional analysis was carried out on transgenic potato tubers of either cultivar (cv.) Record or cv. Desirée to assess the potential for unintended effects caused by the genetic modification process. The range of transgenic lines analysed included those modified in primary carbohydrate metabolism, polyamine biosynthesis and glycoprotein processing. Controls included wildtype tubers, tubers produced from plants regenerated through tissue culture (including a callus phase) and tubers derived from transformation with the 'empty vector' i.e. no specific target gene included (with the exception of the kanamycin resistance gene as a selectable marker). Metabolite analysis included soluble carbohydrates, glycoalkaloids, vitamin C, total nitrogen and fatty acids. Trypsin inhibitor activity was also assayed. These cover the major compounds recommended by the OECD in their Consensus Document on Compositional Considerations for New Varieties of Potatoes: Key Food and Feed Nutrients, Anti-Nutrients and Toxicants (2002). Data was statistically analysed using analysis of variance (ANOVA) for individual compounds and, where applicable, principal component analysis (PCA). In general, targeted compositional analysis revealed no consistent differences between GM lines and respective controls. No construct specifically induced unintended effects. Statistically significant differences between wildtype controls and specific GM lines did occur but appeared to be random and not associated with any specific construct. Indeed such significant differences were also found between wildtypes and both tissue culture derived tubers and tubers derived from transformation with the empty vector. This raises the possibility that somaclonal variation (known to occur significantly in potato, depending on genotype) may be responsible for an unknown proportion of any differences observed between specific GM lines and the wildtype. The most obvious differences seen in GC-MS profiles were between the two potato varieties used in the study.

Alkaloids↗
PubMed1978

Selective denaturation of several yeast enzymes by free fatty acids.

The denaturation of eight purified yeast enzymes, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase, alcohol dehydrogenase, beta-fructosidase, hexokinase and glucose-6-phosphate isomerase, promoted under controlled conditions by the free fatty acids myristic and oleic, is selective. Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADP+ 1 oxidoreductase, EC 1.1.1.49) is extremely sensitive to destabilization and was studied in greater detail. Results show that chain length and degree of unsaturation of fatty acids are important to their destabilizing effect, and that ligands of the enzyme can afford protection. The denaturation process results in more than one altered form. These results can be viewed in the perspective of the possibility that amphipathic substances, and in particular free fatty acids, may play a role for enzyme degradation in vivo, by initiating steps of selective denaturation.

Alcohol Oxidoreductases↗
PubMedDate not supplied

Differences in codon usage among genes encoding proteins of different function in Rhodobacter capsulatus.

Codon usage in Rhodobacter was evaluated and found to be strikingly different from that in Escherichia coli. While codon usage for genes concerned with nitrogen utilization and carotenoid biosynthesis corresponded to expectation, based on codon usage for Rhodobacter in general, that for the fructose utilization (fru) operon and for the photosynthetic genes encoding the reaction centre and light harvesting proteins exhibited significant deviation from expectation and from each other for specific amino acids. The differences in codon usage for the fru operon versus the photosynthetic genes may reflect different proportions of the various tRNA specific for certain amino acids when cells are grown under heterotrophic versus phototropic conditions. In addition, preferential use of the initiation codon, GTG, was found for the first cistrons of Rhodobacter operons.

Base Sequence↗
PubMed2004

The mannitol cycle in Pleurotus ostreatus (Florida).

In mushroom, presence of the mannitol cycle has not been reported so far although the polyol is supposed to be generated by the reduction of fructose by mannitol dehydrogenase. This study submits evidence for the presence of the mannitol cycle in Pleurotus ostreatus. The key enzyme of the cycle, mannitol-1-phosphate dehydrogenase (M1PDH), was present appreciably in all the developmental stages of the mushroom. However, the enzyme level dropped significantly at the onset of sporulation. The presence of M1DPH was confirmed by isozyme analysis and RT-PCR mediated amplification of a approximately 400 bp DNA fragment.

Electrophoresis, Polyacrylamide Gel↗
PubMed2005

Genes required for fructose metabolism are expressed in Purkinje cells in the cerebellum.

Since 1967, fructose has become the primary commercial sweetener in the food industry. Large amounts of fructose can be toxic and have been correlated with atherosclerosis, malabsorption, hyperuricemia, lactic acidosis, and cataracts. To understand the deleterious and critical role(s) fructose plays in normal metabolism, it is essential to know how and where fructose is metabolized. The fructose transporter, GLUT5, and the specialized enzymes ketohexokinase, aldolase, and triokinase comprise the well-defined fructose-specific metabolic pathway found in liver, kidney, and small intestine. It is estimated that 50-70% of ingested fructose is metabolized in these tissues; where and how the remaining 30-50% is metabolized is not well defined. Prediction of tissues capable of metabolizing fructose via this pathway was done using expressed sequence tags (ESTs) in Unigene and a gene-specific virtual northern blot (VNB) algorithm. Unigene and VNB combined correctly predicted the expression of the genes required for fructose metabolism in liver, kidney, and small intestine. Both methods indicated brain, breast, lymphocytes, muscle, placenta, and stomach additionally express this set of genes. Expression of the genes for GLUT5 (glut5) and ketohexokinase (khk) in neurons was validated by immunohistochemistry and RNA in situ hybridization, respectively. Using stringent controls, clear expression of glut5 and khk was localized to Purkinje cells in the cerebellum. Cerebellum was used to oxidize fructose to carbon dioxide. Together, these data suggest that these neurons in the brain are able to utilize fructose as a carbon source.

Animals↗
PubMed1994

Hexose-6-kinases in germinating honey locust cotyledons: substrate specificity of D-fructo-6-kinase.

Extracts of the cotyledons of germinated honey locust (Gleditsia triacanthos) seeds, which contain galactomannan as a reserve polysaccharide in the endosperm, were fractionated by chromatography and the fractions examined for the presence of a specific manno-6-kinase which could phosphorylate the D-mannose released by hydrolysis of galactomannan. One particulate hexokinase (the major hexose-6-kinase fraction) and two soluble hexokinase fractions (the minor portion), as well as a soluble fructo-6-kinase fraction, were initially separated. From chromatography, electrophoresis and kinetic studies, no evidence for a specific manno-kinase was obtained. This and the level and kinetic behaviour of the particulate hexokinase implicated it as the enzyme catalysing the phosphorylation of released D-mannose. The fructo-kinase activity was further separated into three fractions. Kinetic studies on one of these with native and synthetic substrates indicated that the structural requirements for the monosaccharide substrate were a beta-D-anomeric 2-OH in the furanose ring, a 4-OH trans to the D-5-CH2OH and a -CH2OH substituent on C2 (trans to the 5-CH2OH) which could be modified. The orientation of the hydroxyl on C-3 had only a limited effect.

Carbohydrate Sequence↗
PubMed2002

Minor participation of cAMP on the protein kinase phosphorylation of mitochondrial and cytosolic fractions from Ascaris suum: a comparative study with porcine heart muscle.

In contrast to porcine heart muscle in which cAMP effectively activated the phosphorylation of cytosolic proteins, cAMP exerted a minor effect on the phosphorylation of proteins from the soluble fraction of Ascaris suum muscle. Similarly, cAMP did not enhance the kinase activity in the mitochondrial membranes from porcine heart and A. suum, although major differences in protein phosphorylation were observed between both fractions. However, cAMP-dependent protein kinases (PKA) were evidenced in the parasitic soluble mitochondrial fraction, since the phosphorylation of histone IIA and kemptide was augmented in this fraction, in the presence of cAMP. An increase in the phosphorylation of exogenously added A. suum phosphofructokinase was also obtained when cAMP was added to the parasite soluble mitochondrial fraction. The phosphorylation of phosphofructokinase by this fraction was inhibited when kemptide and cAMP were included in the reaction mixture, suggesting substrate competition for the same PKA. Although PKI (6-22), a reported inhibitor of the catalytic subunit of mammalian cAMP-dependent PKAs, did not affect the endogenous phosphorylation of proteins in the various A. suum fractions, an inhibition on the phosphorylation of exogenously added kemptide and phosphofructokinase was observed when PKI (6-22) was incubated with the parasite mitochondrial soluble fraction.

Animals↗
PubMed1982

Phosphoenolpyruvate-dependent fructose phosphotransferase system of Rhodopseudomonas sphaeroides: purification and physicochemical and immunochemical characterization of a membrane-associated enzyme I.

The phosphotransferase system (PTS) of the phototrophic bacterium Rhodopseudomonas sphaeroides consists of a component located in the cytoplasmic membrane and a membrane-associated enzyme called "soluble factor" (SF) [Saier, M. H., Feucht, B. U., & Roseman, S. (1971) J. Biol. Chem. 246, 7819--7821]. SF has been partially purified by a combination of hydrophobic interaction and ion-exchange and gel-permeation chromatography. SF is similar to Escherichia coli enzyme I in its molecular characteristics and enzymatic properties. It has a molecular weight of 85 000 and readily dimerizes. Phosphoenolpyruvate and Mg2+ stabilize the dimer. The enzyme catalyzes the conversion of phosphoenolpyruvate into pyruvate and becomes phosphorylated in the process. The phosphoryl group is subsequently transferred to fructose in the presence of R. sphaeroides membranes. SF substitutes for E. coli enzyme I in fructose or glucose phosphorylation with E. coli enzyme II and HPr. The activities of SF with the R. sphaeroides PTS and the E. coli PTS reside on structurally distinct molecules as shown by their response to limited proteolytic digestion and by immunochemical studies. The activity of SF with the E. coli PTS arises during the isolation procedure and is most likely due to the removal of HPr-like protein from SF.

Chromatography↗
PubMed1998

A comparison of the activities of certain enzymes related to energy metabolism in leukocytes in dogs and cats.

The activities of Na+,K(+)-ATPase in plasma membrane, of cytosolic enzymes and of glutamate dehydrogenase (GlGD) in mitochondria were measured in leukocytes (WBC) from dogs and cats to clarify the differences in energy metabolism in these cells. Feline WBC had significantly higher activities of hexokinase (HK), pyruvate kinase (PK) and LDH with pyruvate as substrate than did canine WBC. Canine WBC had significantly higher activities of glucokinase (GK) and GlDH than did feline WBC. Feline WBC had unique characteristics of energy metabolism in that the activities of the cytosolic enzymes under anaerobic conditions were significantly higher than those in canine WBC. It therefore appears that there are distinct differences in glucose-metabolism in WBC between dogs and cats. WBC enzyme activities are considered to reflect the metabolic state in the whole body of the animal. It is therefore suggested that changes in the activities of certain glycolytic enzymes in WBC may be useful as a diagnostic indicator in some types of metabolic disease in dogs and cats.

Alanine Transaminase↗
PubMed1985

The purification and properties of human liver ketohexokinase. A role for ketohexokinase and fructose-bisphosphate aldolase in the metabolic production of oxalate from xylitol.

Ketohexokinase (EC 2.7.1.3) was purified to homogeneity from human liver, and fructose-bisphosphate aldolase (EC 4.1.2.13) was partially purified from the same source. Ketohexokinase was shown, by column chromatography and polyacrylamide-gel electrophoresis, to be a dimer of Mr 75000. Inhibition studies with p-chloromercuribenzoate and N-ethylmaleimide indicate that ketohexokinase contains thiol groups, which are required for full activity. With D-xylulose as substrate, ketohexokinase and aldolase can catalyse a reaction sequence which forms glycolaldehyde, a known precursor of oxalate. The distribution of both enzymes in human tissues indicates that this reaction sequence occurs mainly in the liver, to a lesser extent in the kidney, and very little in heart, brain and muscle. The kinetic properties of ketohexokinase show that this enzyme can phosphorylate D-xylulose as readily as D-fructose, except that higher concentrations of D-xylulose are required. The kinetic properties of aldolase show that the enzyme has a higher affinity for D-xylulose 1-phosphate than for D-fructose 1-phosphate. These findings support a role for ketohexokinase and aldolase in the formation of glycolaldehyde. The effect of various metabolites on the activity of the two enzymes was tested to determine the conditions that favour the formation of glycolaldehyde from xylitol. The results indicate that few of these metabolites affect the activity of ketohexokinase, but that aldolase can be inhibited by several phosphorylated compounds. This work suggests that, although the formation of oxalate from xylitol is normally a minor pathway, under certain conditions of increased xylitol metabolism oxalate production can become significant and may result in oxalosis.

Electrophoresis, Polyacrylamide Gel↗
PubMed1993

Expression of rat liver ketohexokinase in yeast results in fructose intolerance.

Rat liver ketohexokinase (ATP:D-fructose 1-phosphotransferase; EC 2.7.1.3) was purified to homogeneity and the molecular mass of the protein was found by mass spectrometry to be 32,800 Da. The enzyme was cleaved and the amino acid sequences of seven peptides, comprising 24% of the total sequence, were determined. This sequence information was used to design oligonucleotide primers for a PCR using rat liver single-stranded cDNA as a template. The 224 bp PCR product was used as a probe to screen a rat liver cDNA library. A cDNA sequence of 1342 bp was obtained from three positive clones. This contained the entire coding region for ketohexokinase, and all seven peptides were identified in the predicted amino acid sequence. When ketohexokinase was expressed in Saccharomyces cerevisiae using the yeast expression vector pMA91, the cells became intolerant of the presence of fructose in their growth media. The growth of an exponential-phase culture was completely arrested within 90 min by the addition of fructose to a final concentration as low as 0.1% (w/v). This response is associated with an accumulation of fructose 1-phosphate. The cDNA for ketohexokinase encodes a protein composed of 299 amino acids with a combined molecular mass of 32,728 Da. This is in close agreement with the value for the isolated protein determined by mass spectrometry. The primary structure does not show any significant homology with those of other eukaryotic hexokinases, but it contains a highly conserved region that is present in three prokaryotic phosphotransferases that have furanose substrates.

Amino Acid Sequence↗
PubMed2001

Genetic control of manno(fructo)kinase activity in Escherichia coli.

Mutants of Escherichia coli unable to use fructose by means of the phosphoenolpyruvate/glycose phosphotransferase system mutate further to permit growth on that ketose by derepression of a manno(fructo)kinase (Mak(+) phenotype) present in only trace amounts in the parent organisms (Mak-o phenotype). The mak gene was located at min 8.8 on the E. coli linkage map as an ORF designated yajF, of hitherto unknown function; it specifies a deduced polypeptide of 344 aa. The derepression of Mak activity was associated with a single base change at position 71 (codon 24) of the gene, where GCC (alanine) in Mak-o has been changed to GAC (aspartate) in Mak(+). By cloning selected portions of the total 1,032-bp mak gene into a plasmid that also carried a temperature-sensitive promoter, we showed that the mutation resided in a 117-bp region that does not specify sequences necessary for Mak activity but was located 46 bp upstream of a 915-bp portion that does. Mak(+) and Mak-o strains differ greatly in the heat stability of the enzyme: at 61 degrees C, mak-o cloned into a mak-o recipient loses 50% of its activity in approximately 6 min, whereas it takes over 30 min to achieve a similar reduction in the activity of mak(+) cloned into a mak-o strain. However, the Mak activity of the cloned fragment specifying the enzyme without the regulatory region lost activity with a half-life of 29 min irrespective of whether it was derived from a mak(+) or a mak-o donor, which indicates that the A24D mutation contributes to the high enzyme activity of Mak(+) mutants by serving to protect Mak from denaturation.

Chromosome Mapping↗
PubMed2005

Eucalyptus leaf extract inhibits intestinal fructose absorption, and suppresses adiposity due to dietary sucrose in rats.

Sucrose is more lipogenic than starch, and the extreme ingestion of sucrose induces adiposity and obesity. The aim of this study was to examine the effect of the eucalyptus (Eucalyptus globulus) leaf extract (ELE) on adiposity due to dietary sucrose in rats. In addition, in this study, the effect of ELE on intestinal fructose absorption was also examined. Rats were fed a high-sucrose diet (75 % in calorie base) with or without ELE (10 g/kg diet) for 5 weeks. Body weight was lower in the rats receiving ELE than in the controls (342 (sd 37.9) v. 392 (sd 26.0) g (n 7); P<0.05). Furthermore, ELE resulted in decreases in the triacylglycerol concentrations in the plasma (1.44 (sd 0.448) v. 2.79 (sd 0.677) mmol/l (n 7); P<0.05) and liver (19.1 (sd 5.07) v. 44.1 (sd 16.28) micromol/g (n 7); P<0.05). In contrast, ELE did not show any significant effects in the rats fed a starch diet. When rats were orally given ELE 10 min before fructose administration, the intestinal fructose absorption, which was examined by measuring the elevated concentration of fructose in the portal vein at 30 min after the fructose administration, was significantly inhibited in a dose-dependent manner. Furthermore, in rats fed a high-fructose diet, the plasma and hepatic triacylglycerol concentrations were significantly decreased by ELE. These results indicate that ELE, which inhibits the intestinal fructose absorption, can suppress adiposity in rats that ingest large amounts of sucrose or fructose.

Absorption↗
PubMed1998

Metabolism is required for chemotaxis to sugars in Rhodobacter sphaeroides.

Chemotaxis towards carbohydrates is mediated, in enteric bacteria, either by the transport-independent, methylation-dependent chemotaxis pathway or by transport and phosphorylation via the phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS). This study shows that Rhodobacter sphaeroides is chemotactic to a range of carbohydrates but the response involves neither the classical methyl-accepting chemotaxis protein (MCP) pathway nor the PTS transport pathway. The chemoattractant fructose was transported by a fructose-specific PTS system, but transport through this system did not appear to cause a chemotactic signal. Chemotaxis to sugars was inducible and occurred with the induction of carbohydrate transport systems and with substrate incorporation. A mutation of the glucose-6-phosphate dehydrogenase gene (zwf) inhibited chemotaxis towards substrates metabolized by this pathway although transport was unaffected. Chemotaxis to other, unrelated, chemoattractants (e.g. succinate) was unaffected. These data, in conjunction with the fact that mannitol and fructose (which utilize different transport pathways) compete in chemotaxis assays, suggest that in R. sphaeroides the chemotactic signal is likely to be generated by metabolic intermediates or the activities of the electron-transport chain and not by a cell-surface receptor or the rate or mode of substrate transport.

Biological Transport↗