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PubMed2004

Presteady-state kinetic evidence for a ring-opening activity in fructose-1,6-(bis)phosphate aldolase.

Fructose 1,6-bisphosphate aldolase, a glycolytic enzyme, catalyzes the cleavage of fructose 1,6-bisphosphate, resulting in two three-carbon products. The reaction of the class I enzymes, which utilize a Schiff-base intermediate, requires that the hexose be in the open-chain form. This form comprises only 1-2% of the sugar at equilibrium. The chemical form of the substrate that binds to aldolase and begins the catalytic cycle has not been unequivocally demonstrated. Transient-state kinetics in single-turnover experiments of fructose 1,6-bisphosphate with aldolase in excess reveals the rates of the intermediate steps in the cleavage reaction, including those from initial binding to Schiff-base formation. The rate of hexose Schiff-base formation was faster than the uncatalyzed rate for ring-opening of either the alpha- or beta-furanose at 4 degrees C. In addition, approach-to-equilibrium experiments reveal that aldolase binds and reacts first with 70% of fructose-1,6-bisphosphate in a fast reaction, consistent with the amount of beta-anomer in solution, and with the remaining 30%, presumably the alpha-anomer, in a slow reaction. These results indicate that aldolase must catalyze the ring-opening step and that there may be a previously unrecognized second active site on the enzyme for catalyzing this reaction.

Fructose-Bisphosphate Aldolase↗
PubMed2003

4-hydroxy-2,5-dimethyl-3(2H)-furanone formation by Zygosaccharomyces rouxii: effect of the medium.

The formation of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) by Zygosaccharomyces rouxii was studied in yeast-peptone-dextrose medium containing d-fructose 1,6-diphosphate under various culture conditions. Cell growth and HDMF production was heavily dependent on medium pH and sodium chloride concentration. Higher pH values of the nutrient medium had a positive effect on HDMF formation but retarded cell growth resulting in an optimal pH value of 5.1 with regard to the yield of HDMF. Salt stress stimulated HDMF formation by Z. rouxii as increasing sodium chloride concentration led to higher amounts of HDMF. The HDMF concentration in the culture supernatant and HDMF formation per yeast cell peaked at 20% sodium chloride in the nutrient medium. The nonutilizable carbohydrate d-xylose displayed a weak effect on HDMF formation, and the addition of glycerol to salt-stressed cells had no effect on the production of HDMF.

Culture Media↗
PubMedDate not supplied

Characterization of vacuolar membrane proteins changed in rice root treated with gibberellin.

Rice vacuolar membrane proteins changed by gibberellin (GA) were analyzed using a proteome approach. Vacuolar membrane fractions were isolated using a discontinuous sucrose/sorbitol system and 10 proteins increased in vacuolar membrane of the root, treated with GA(3) as compared with control. Fructose-1,6-bisphosphate aldolase C-1 and vacuolar H(+)-ATPase (V-ATPase) increased in root vacuolar membrane by GA(3) interacted in rice roots. It suggests that aldolase C-1 regulates the V-ATPase mediated control of cell elongation that determines root growth.

Adenosine Triphosphatases↗
PubMed1998

In vitro induction of nitric oxide by fructose-1,6-diphosphate in the cardiovascular system of rats.

Nitric oxide (NO) functions as a cellular messenger in a number of organs and cell systems in the cardiovascular system (CVS); it is a significant determinant of basal vascular tone and regulates myocardial contractility and platelet aggregation. The present study focused upon understanding the in vitro effects of fructose-1,6-diphosphate (FDP) on the rat cellular NO pathway. The iNOS activity was measured by monitoring the formation of (3H)-citrulline in 50,000 g soluble fractions of crude homogenates of endothelial (ET) and smooth muscle cells (SMC) from the arteries of rats, and macrophages (MAC) and lymphocytes (LYM) from rat blood. FDP in concentrations of 10-1000 microM stimulated rat cellular iNOS activity in a concentration-dependent manner. FDP-stimulated rat cellular iNOS was found to be completely reversed by 5 microM concentration of NG-monomethyl-L-arginine (L-NMMA), the potent mammalian NOS inhibitor. These studies demonstrated that FDP may induce the formation of NO by stimulating rat cardiovascular iNOS activity.

Animals↗
PubMed2000

Membrane permeability of fructose-1,6-diphosphate in lipid vesicles and endothelial cells.

Fructose-1,6-diphosphate (FDP) is a glycolytic intermediate which has been used an intervention in various ischemic conditions for two decades. Yet whether FDP can enter the cell is under constant debate. In this study we examined membrane permeability of FDP in artificial membrane bilayers and in endothelial cells. To examine passive diffusion of FDP through the membrane bilayer, L-alpha-phosphatidylcholine from egg yolk (Egg PC) (10 mM) multi-lamellar vesicles were created containing different external concentrations of FDP (0, 0.5, 5 and 50 mM). The passive diffusion of FDP into the vesicles was followed spectrophotometrically. The results indicate that FDP diffuses through the membrane bilayer in a dose-dependent fashion. The movement of FDP through Egg PC membrane bilayers was confirmed by measuring the conversion of FDP to dihydroxyacetone-phosphate and the formation of hydrozone. FDP (0, 0.5, 5 or 50 mM) was encapsulated in Egg PC multilamellar vesicles and placed in a solution containing aldolase. In the 5 and 50 mM FDP groups there was a significant increase in dihydroxyacetone/hydrazone indicating that FDP crossed the membrane bilayer intact. We theorized that the passive diffusion of FDP might be due to disruption of the membrane bilayer. To examine this hypothesis, small unilamellar vesicles composed of Egg PC were created in the presence of 60 mM carboxyfluorescein, and the leakage of the sequestered dye was followed upon addition of various concentrations of FDP, fructose, fructose-6-phosphate, or fructose-1-phosphate (0, 5 or 50 mM). These results indicate that increasing concentrations of FDP increase the leakage rate of carboxyfluorescein. In contrast, no concentration of fructose, fructose-6-phosphate, or fructose-1-phosphate resulted in any significant increase in membrane permeability to carboxyfluorescein. To examine whether FDP could pass through cellular membranes, we examined the uptake of 14C-FDP by endothelial cells cultured under hypoxia or normoxia for 4 or 16 h. The uptake of FDP was dose-dependent in both the normoxia and hypoxia treated cells, and was accompanied by no significant loss in endothelial cell viability. Our results demonstrate that FDP can diffuse through membrane bilayers in a dose-dependent manner.

Cell Hypoxia↗
PubMed2001

The uptake and metabolism of fructose-1,6-diphosphate in rat cardiomyocytes.

Fructose-1,6-diphosphate (FDP) is a glycolytic intermediate which has been theorized to increase the metabolic activity of ischemic tissues. Here we examine the effects of externally applied FDP on cardiomyocyte uptake and metabolism. Adult rat cardiomyocytes were isolated and exposed to varying concentrations (0, 5, 25 and 50 mM) of FDP for either 1, 16 or 24 h of hypoxia (95% N2/5% CO2), each time period followed by a 1 h reoxygenation (95% air/5% CO2). The uptake of FDP by rat cardiomyocytes was more concentration-dependent than time-dependent. Furthermore, the uptake of FDP by the cardiomyocytes was similar in the hypoxia and normoxia treated cells. Alamar Blue, a redox indicator that is sensitive to metabolic activity, was used to monitor the effects of the FDP on cardiomyocyte metabolism. In the 1 h hypoxia or normoxia group, the 5, 10 and 25 mM FDP showed a significant increase in metabolism compared to the control cells. When the length of hypoxia was extended to 16 h, all doses of FDP were greater than control. And at the 24 h hypoxia or normoxia time period, only the 10, 25 and 50 mM FDP groups were greater than control. The results indicate a non-linear trend between the external concentration of FDP and the changes noted in metabolism. The findings from this study indicate that a narrow concentration range between 5-10 mM augments cardiomyocyte metabolism, but higher or lower doses may have little additional affect.

Animals↗
PubMed2002

Fructose-1,6-Bisphosphate inhibits excess activation of Kupffer cell function induced by endotoxin.

The effect and mechanism of action of fructose-1,6-bisphosphate (FBP) on Kupffer cell activation were studied in vitro. Kupffer cell was activated by isolation procedure alone from the hepatic tissue. In cultured rat Kupffer cells stimulated by endotoxin, treatment with 5-20 mM FBP not only preserved phagocytic activity, but also inhibited secretion of cytokines (tumor necrosis factor-a and interleukin-1beta) and production of nitric oxide (NOx). Moreover, treatment with 10 mM FBP suppressed the elevation in the intracellular Ca2+ concentration on Kupffer cells stimulated by phorbol 12-myristate 13-acetate, which suggested that this effect may be one of the agents that limit the activation of Kupffer cells. The administration of FBP was effective in the prevention of endotoxin-induced hepatopathy, and we suggest that this may have useful clinical applications.

Animals↗
PubMed2002

Time dependent responses of glycolytic intermediates in a detailed glycolytic model of Lactococcus lactis during glucose run-out experiments.

Glucose addition and subsequent run-out experiments were compared to simulations with a detailed glycolytic model of Lactococcus lactis. The model was constructed largely on bases of enzyme kinetic data taken from literature and not adjusted for the specific simulations shown here. Upon glucose depletion a rapid increase in PEP, inorganic phosphate and a gradual decrease in fructose 1,6-bisphosphate (FBP) were measured and predicted by simulation. The dynamic changes in these and other intermediate concentrations as measured in the experiments were well predicted by the kinetic model.

Adenosine Triphosphate↗
PubMed2002

Implication of guanosine 3',5'-cyclic monophosphate, adenosine 3',5'-cyclic monophosphate, adenosine 5'-mono-, di- and triphosphate and fructose-2,6-bisphosphate in the regulation of the glycolytic pathway in hypoxic/anoxic mussel, Mytilus galloprovincialis.

The change in the content of cyclic GMP, cyclic AMP, ATP, ADP, AMP and fructose-2,6-bisphosphate that occurred in the mantle of the mussel Mytilus galloprovincialis Lmk when specimens of this mollusk were subjected to a hypoxia/anoxia situation were assessed. After the early 24 h in anaerobiosis, a clear decrease was observed in the ATP content, which remained close to that value for the rest of the time. AMP content doubled during the early 24 h in anaerobiosis and, from that time on, it remained close to that value. Fructose-2,6-bisphoshate and cyclic GMP showed a similar behavior. The levels of these compounds rose significantly during the early hours in anaerobiosis, and then fell to values similar to those of aerobiosis, remaining constant for the rest of the time. Neither ADP nor cAMP showed significant variations.

Adenosine Diphosphate↗
PubMed2001

Differential distribution of aldolase A and C in the human central nervous system.

We have analyzed the distribution of aldolase A and C mRNAs and proteins in various areas of the human brain using Northern blot analyses and immunohistochemistry. Aldolase A mRNA expression was higher than aldolase C mRNA expression in all areas of the brain examined. Aldolase C mRNA expression was highest in the cerebellum. Aldolase C protein was present in well-delimited regions of the CNS, and was distributed in stripes in the Purkinje cell layer of the cerebellum, in the inferior olives and in the sensory neurons of the posterior horn of the spinal cord. The novel finding of aldolase C in well-delimited cell compartments of the human cerebellum and in several other areas of the CNS lends weight to the hypothesis that this protein exerts other functions (e.g. sensory transmission) besides those characteristic of a glycolytic enzyme.

Afferent Pathways↗
PubMed2003

Implication of adenosine 3',5'-cyclic monophosphate, guanosine 3',5'-cyclic monophosphate, adenosine 5'-mono-, di-, and triphosphate and fructose-2,6-bisphosphate in the regulation of the glycolytic pathway in relation to the gametogenic cycle in the mussel mytilus galloprovincialis Lmk.

The changes in the contents of cyclic AMP, cyclic GMP, ATP, ADP, AMP and fructose-2,6-bisphosphate that occur in the mantle tissue of the mussel Mytilus galloprovincialis Lmk were analysed with regard to the annual gametogenic cycle. Throughout 2 years, the lowest contents of AMP, ADP and ATP were detected during late winter-spring, whereas the maximum appeared in the autumn months. During the second year, fructose-2,6-bisphosphate and cAMP showed a very similar behaviour. The levels of both compounds rose throughout the year until a maximum in September. Their behaviour was also similar to that observed during the first year, but displaced in time. Both in 1998 and in 1999, the highest level of cGMP was detected during the spring-summer months. The results obtained suggest that the glycolytic pathway, with regard to the breeding cycle, might be regulated by fructose-2,6-bisphosphate and cyclic AMP through the activation of 6-phosphofructo-1-kinase, which is the main regulating enzyme of the glycolysis in mantle of M. galloprovincialis.

Adenosine Diphosphate↗
PubMed2004

Permeability of fructose-1,6-bisphosphate in liposomes and cardiac myocytes.

Fructose-1,6-bisphosphate (FBP) helps preserve heart and other organs under ischemic conditions. Previous studies indicated that it can be taken up by various cell types. Here we extended observations from our group that FBP could penetrate artificial lipid bilayers and be taken up by cardiac myocytes, comparing the uptake of FBP to that of L-glucose. Using liposomes prepared by the freeze-thaw method, FBP entered about 200-fold slower than L-glucose. For liposomes of either soybean or egg lipids, 50 mM FBP enhanced the permeability of FBP itself, with little effect on general permeability (measured by uptake of L-glucose). In experiments with isolated cardiac myocytes at 21 degrees C, FBP uptake exceeded the uptake of L-glucose by several fold and appeared to equilibrate by 60 min. There was both a saturable component at micromolar levels and a nonsaturable component which dominated at millimolar levels. The saturable component was inhibited by Pi and by other phosphorylated sugars, though with lower affinity than FBP. Both saturable and nonsaturable uptakes were also observed at 3 degrees C. The results indicate that FBP enters myocytes not by simple penetration through the lipid bilayer, but via at least two distinct protein-dependent processes. The uptake could lead to intracellular effects important in hypothermic heart preservation.

Animals↗
PubMed2004

Mayaro virus infection alters glucose metabolism in cultured cells through activation of the enzyme 6-phosphofructo 1-kinase.

Although it is well established that cellular transformation with tumor virus leads to changes on glucose metabolism, the effects of cell infection by non-transforming virus are far to be completely elucidated. In this study, we report the first evidence that cultured Vero cells infected with the alphavirus Mayaro show several alterations on glucose metabolism. Infected cells presented a two fold increase on glucose consumption, accompanied by an increment in lactate production. This increase in glycolytic flux was also demonstrated by a significant increase on the activity of 6-phosphofructo 1-kinase, one of the regulatory enzymes of glycolysis. Analysis of the kinetic parameters revealed that the regulation of 6-phosphofructo 1-kinase is altered in infected cells, presenting an increase in Vmax along with a decrease in Km for fructose-6-phosphate. Another fact contributing to an increase in enzyme activity was the decrease in ATP levels observed in infected cells. Additionally, the levels of fructose 2,6-bisphosphate, a potent activator of this enzyme, was significantly reduced in infected cells. These observations suggest that the increase in PFK activity may be a compensatory cellular response to the viral-induced metabolic alterations that could lead to an impairment of the glycolytic flux and energy production.

Adenosine Triphosphate↗
PubMed2003

Fructose-2,6-bisphosphate contents were increased in response to salt, water and osmotic stress in leaves of Bruguiera gymnorrhiza by differential changes in the activity of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphate 2-phosphatase.

The steady-state level of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphate 2-phosphatase (F6P2K/F26BPase) transcript has been found to be raised in the mangrove Bruguiera gymnorrhiza treated with 500 mM NaCl for 6 h. In the present study, we assayed both F6P2K/F26BPase activity and fructose-2,6-bisphosphate (F26BP) contents in leaves of salt- and water-stressed B. gymnorrhiza. In the plants treated with 500 mM NaCl, no increase in transcript level was observed after 1 day of treatment, while both the ratio between F6P2K and F26BPase activity (K/P ratio) and leaf F26BP level were about two-fold higher than in control plants. Several water stress-associated treatments, including 500 mM NaCl treatment for 6 h, 1 M mannitol treatment for 6 h and dehydration treatment, resulted in increases in leaf F26BP level as compared with water-grown plants. The raised levels of F26BP in osmotically stressed plants treated with NaCl and mannitol were accompanied with increased transcript levels and subsequent increases in both F6P2K and F26BPase activities, while the increase in F26BP levels in dehydrated plants was attributed to an increase in K/P ratio without an increase in transcript levels. These results suggest that, although both treatments resulted in increases in F26BP levels, B. gymnorrhiza differentially responds to osmotic stress and water stress.

Abscisic Acid↗
PubMed1989

Fructose-1,6-bisphosphate protects astrocytes from hypoxic damage.

To determine the effects of glucose and fructose-1,6-bisphosphate (FDP) on hypoxic cell damage, primary cultures of astrocytes were incubated for 18 h in an air-tight chamber that had been flushed with 95% N2/5% CO2 for 15 min before it was sealed. Cultures containing 7.5 mM glucose without FDP or FDP without glucose showed evidence of significant cell injury after 18 h of hypoxia (increased lactate dehydrogenase content in the culture medium; cell edema and disruption by phase-contrast microscopy). Cultures exposed to glucose + FDP had normal lactate dehydrogenase concentrations and appeared normal microscopically. Maximal protection of hypoxic cells occurred at 6.0 mM FDP. Lactate concentrations of the culture medium of hypoxic cells increased 2.5 times above normoxic control values when glucose was present, but neither FDP alone nor glucose + FDP caused the lactate concentrations to increase further. This implies that anaerobic glycolysis was not increased by adding FDP to the medium. Cell volumes (water space) measured with [14C]-3-0-methyl-D-glucose were normal with glucose + FDP in the culture medium of hypoxic cells but were significantly larger than normal when glucose alone was present. Increases in cell volume paralleled changes in lactate dehydrogenase in the culture medium. Uptake of [14C]FDP occurred rapidly in normoxic cells and was maximal after 5 min of incubation. The data indicate that the presence of glucose + FDP in the culture medium protects primary cultures of hypoxic astrocytes from cell damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1994

T and R states in the crystals of bacterial L-lactate dehydrogenase reveal the mechanism for allosteric control.

The crystal structure of L-lactate dehydrogenase from Bifidobacterium longum, determined to 2.5 A resolution, contains a regular 1:1 complex of T- and R-state tetramers. A comparison of these two structures within the same crystal lattice and kinetical characterization of the T-R transition in solution provide an explanation for the molecular mechanism of allosteric activation. Substrate affinity is controlled by helix sliding between subunits which is triggered by the binding of the activator, fructose 1,6-bisphosphate. The proposed mechanism can explain activation by chemical modification and mutagenesis, as well as suggesting why vertebrate counterparts are not allosteric.

Allosteric Regulation↗
PubMed1997

Crystal structure of a trapped phosphoenzyme during a catalytic reaction.

The crystal structure of the fructose-2,6-bisphosphatase domain trapped during the reaction reveal a phosphorylated His 258, and a water molecule immobilized by the product, fructose-6-phosphate. The geometry suggests that the dephosphorylation step requires prior removal of the product for an 'associative in-line' phosphoryl transfer to the catalytic water.

Animals↗
PubMed1999

Magnetic resonance detects metabolic changes associated with chemotherapy-induced apoptosis.

Apoptosis was induced by treating L1210 leukaemia cells with mechlorethamine, and SW620 colorectal cells with doxorubicin. The onset and progression of apoptosis were monitored by assessing caspase activation, mitochondrial transmembrane potential, phosphatidylserine externalization, DNA fragmentation and cell morphology. In parallel, 31P magnetic resonance (MR) spectra of cell extracts were recorded. In L1210 cells, caspase activation was detected at 4 h. By 3 h, the MR spectra showed a steady decrease in NTP and NAD, and a significant build-up of fructose 1,6-bisphosphate (F-1,6-P) dihydroxyacetonephosphate and glycerol-3-phosphate, indicating modulation of glycolysis. Treatment with iodoacetate also induced a build-up of F-1,6-P, while preincubation with two poly(ADP-ribose) polymerase inhibitors, 3-aminobenzamide and nicotinamide, prevented the drop in NAD and the build-up of glycolytic intermediates. This suggested that our results were due to inhibition of glyceraldehyde-3-phosphate dehydrogenase, possibly as a consequence of NAD depletion following poly(ADP-ribose) polymerase activation. Doxorubicin treatment of the adherent SW620 cells caused cells committed to apoptosis to detach. F-1,6-P was observed in detached cells, but not in treated cells that remained attached. This indicated that our observations were not cell line- or treatment-specific, but were correlated with the appearance of apoptotic cells following drug treatment. The 31P MR spectrum of tumours responding to chemotherapy could be modulated by similar effects.

Animals↗