The periodate oxidation of sucrose in aqueous N,N-dimethylformamide.

Sucrose has been oxidized with sodium periodate in 0-50% aqueous N,N-dimethylformamide (DMF). In 50% aqueous DMF the reaction is selective for the glucose ring, yielding a dialdehyde. The increased selectivity is not due to conformational factors but is ascribed to the dissociation of water from cyclic periodate ester species which makes the reaction via the acyclic ester on fructose unfavourable.     

Sucrose utilization by Zymomonas mobilis: formation of a levan

1. Molar growth-yield coefficients of Zymomonas mobilis for glucose, fructose, glucose plus fructose, and sucrose are reported. Yield coefficients for sucrose are appreciably lower than those for the equivalent concentrations of glucose plus fructose. 2. Only 2.6% of [U-(14)C]glucose supplied in the growth medium is incorporated into cell substance by Z. mobilis utilizing glucose as the energy source. 3. During growth on sucrose a levan is formed. It has been characterized and shown to resemble other bacterial levans. 4. Levan formation from sucrose could be demonstrated with both washed cell suspensions and cell extracts of Z. mobilis. 5. Sucrose phosphorylase could not be demonstrated in extracts of the organism.     

Uptake and phosphorylation of glucose and fructose in Daucus carota cell suspensions are differently regulated

Cell suspensions of Daucus carota L. were grown in batch culture on 50 mM sucrose, 100 mM glucose or 100 mM fructose. Sucrose was rapidly converted extra-cellularly into equimolar amounts of glucose and fructose, and glucose was then taken up preferentially. This impaired uptake of fructose could partially be explained by the eight-fold lower affinity of the hexose carrier in the plasmamembrane for fructose compared to glucose. However, cells grown on fructose as the sole carbon source showed a shorter lag phase and showed more biomass production compared to glucose-grown cells, indicating that conversion of glucose and fructose were also differently regulated. Ninety-five % of the glucose phosphorylating activity was membrane-associated and most probably confined to mitochondria; therefore, it might be present in a respiratory ‘compartment’ making glucose a better substrate for respiration than fructose. The soluble fraction contained the majority of the fructokinase activity. This activity was hypothesized to be more or less randomly distributed through the cytosol; in this soluble ‘compartment’ a pool of fructose-6-phosphate is formed. Concomitantly, via glucose-6-phosphate (G-6-P) and glucose-1-phosphate (G-1-P), it is converted into UDPG-glucose, resulting in structural cell components. The observed transient obstruction of the conversion of G-1-P into UDP-glucose in fructose-grown cells, leading to G-1-P accumulation, might be a result of both an altered equilibrium maintained by phosphoglucomutase, interconverting G-6-P and G-1-P and low levels of nucleotide triphosphates. Low nucleotide triphosphate production, connected with a low initial respiration rate, might be caused by the ten-fold lower affinity of the membrane-associated phosphorylating enzymes for fructose compared to glucose. Our results were taken to indicate that two separate pools of glycolytic intermediates exist in D. carota cells: one distributed throughout the cytosol and one surrounding the mitochondria.     

Plasmid-mediated uptake and metabolism of sucrose by Escherichia coli K-12.

The conjugative plasmid pUR400 determines tetracycline resistance and enables cells of Escherichia coli K-12 to utilize sucrose as the sole carbon source. Three types of mutants affecting sucrose metabolism were derived from pUR400. One type lacked a specific transport system (srcA); another lacked sucrose-6-phosphate hydrolase (scrB); and the third, a regulatory mutant, expressed both of these functions constitutively (scrR). In a strain harboring pUR400, both transport and sucrose-6-phosphate hydrolase were inducible by fructose, sucrose, and raffinose; if a scrB mutant was used, fructose was the only inducer. These data suggested that fructose or a derivative acted as an endogenous inducer. Sucrose transport and sucrose-6-phosphate hydrolase were subject to catabolite repression; these two functions were not expressed in an E. coli host (of pUR400) deficient in the adenosine 3-,5'-phosphate receptor protein. Sucrose uptake (apparent Km = 10 microM) was dependent on the scrA gene product and on the phosphoenolpyruvate-dependent sugar:phosphotransferase system (PTS) of the host. The product of sucrose uptake (via group translocation) was identified as sucrose-6-phosphate, phosphorylated at C6 of the glucose moiety. Intracellular sucrose-6-phosphate hydrolase catalyzed the hydrolysis of sucrose-6-phosphate (Km = 0.17 mM), sucrose (Km = 60 mM), and raffinose (Km = 150 mM). The active enzyme was shown to be a dimer of Mr 110,000.     

Some comparisons among the calming and pain-relieving effects of sucrose, glucose, fructose and lactose in infant rats

Ultrasonic vocalizations were recorded from 10-day-old albinorats while they were isolated from their dam and siblings. Eachrat received a 1.0% BW intra-oral infusion of sucrose, fructose,glucose or lactose at a concentration range of 0.22–0.66M for 3 min and their vocalizations were determined during theinfusion and for an additional 7 min. Sucrose, fructose andglucose all significantly reduced vocalizations to about 50%of baseline levels, whereas lactose, the milk sugar, was ineffective.Moreover, the dose–response function was flat for thethree effective sugars. In a second experiment, the effectsof these sugars on heat escape latency were measured. Sucrose,fructose and glucose each elevated the latency with which infantrats removed a paw from a 48°C surface; lactose did not.These findings of lactose ineffectiveness and the flat dose-responsefunction for the other three sugars exactly parallel those obtainedfor human newborns. Their implications are discussed.     

Effects of dietary fructose on liver steatosis in overfed mule ducks.

Overfeeding of some waterfowl species results in obesity, which is mainly characterized by a dramatic hepatic steatosis induced by strong accumulation of lipids synthesized from dietary glucose in the liver. In mammals, fructose is known to be able to raise plasma triacylglycerol concentrations significantly; consequently, this may induce obesity. The aim of this study was to assess the effect of partial replacement of dietary glucose provided by corn starch with fructose on metabolism and fatty liver production in the Mule ducks. On the basis of 9.5 kg maize (132,920 kJ) given twice a day for 14 days, a supplementation of 9,800 kJ was provided in form of glucose, sucrose or high fructose corn syrup (HFCS: 50 % glucose, 42 % fructose and 8 % other saccharides). Fatty liver weight in ducks fed with glucose supplementation was 499 +/- 21 g. Sucrose or HFCS supplementation brought about a significant increase in liver weight (+ 18.7 % and + 16.3 % vs. glucose supplementation respectively, p < 0.05). These results suggest that the dietary fructose favors the liver steatosis by increasing hepatic lipogenesis. Postprandial plasma insulin concentrations were similar in ducks fed diets with or without fructose, suggesting that the effect of fructose on liver steatosis is not mediated by insulin.     

Enhancement of glycogen concentrations in primary cultures of rat hepatocytes exposed to glucose and fructose.

Glycogen synthesis in isolated hepatocytes can occur from glucose both by a direct mechanism and by an indirect process in which glucose is first metabolized to C3 intermediates before use for glycogenesis via gluconeogenesis. We studied the incorporation into glycogen of glucose and the gluconeogenic substrate, fructose, in primary cultures of hepatocytes from fasted rats. In the presence of insulin, both glucose and fructose promoted net deposition of glycogen; however, fructose carbon was incorporated into glycogen to a greater extent than that from glucose. When glucose and fructose were administered simultaneously, the glycogenic utilization of glucose was stimulated 2-3-fold, and that of fructose was increased by about 50%. At constant hexose concentrations, the total incorporation of carbon, and the total accumulation of glycogen mass, from glucose and fructose when present together exceeded that from either substrate alone. Fructose did not change the relative proportion of glucose carbon incorporated into glycogen via the indirect (gluconeogenic) mechanism. The synergism of glucose and fructose in glycogen synthesis in isolated rat hepatocytes in primary culture appears to result from a decrease in the rate of degradation of newly deposited glycogen, owing to (i) decreased amount of phosphorylase a mediated by glucose and (ii) noncovalent inhibition of residual phosphorylase activity by some intermediate arising from the metabolism of fructose, presumably fructose 1-phosphate.     

Complete Sucrose Metabolism Requires Fructose Phosphotransferase Activity in Corynebacterium glutamicum To Ensure Phosphorylation of Liberated Fructose

Sucrose uptake by Corynebacterium glutamicum involves a phosphoenolpyruvate-dependent sucrose phosphotransferase (PTS), but in the absence of fructokinase, further metabolism of the liberated fructose requires efflux of the fructose and reassimilation via the fructose PTS. Mutant strains lacking detectable fructose-transporting PTS activity accumulated fructose extracellularly but consumed sucrose at rates comparable to those of the wild-type strain.     

Sugar metabolism in germinating soybean seeds: evidence for the sorbitol pathway in soybean axes

Characterization of sugar content and enzyme activity in germinating soybean (Glycine max L. Merrell) seeds led to the discovery of sorbitol accumulating in the axes during germination. The identity of sorbitol was confirmed by relative retention times on high-performance liquid chromatography and gas liquid chromatography and by mass spectra identical with authentic sorbitol. Accumulation of sorbitol in the axes started on day 1 of germination as sucrose decreased and glucose and fructose increased. Sucrose also decreased in the cotyledons, but there was no accumulation of sorbitol, glucose, or fructose. Accumulation of sorbitol and hexoses was highly correlated with increased invertase activity in the axes, but not with sucrose synthase and sucrose phosphate synthase activities. Sucrose synthase activity was relatively high in the axes, whereas the activity of sucrose phosphate synthase was relatively high in the cotyledons. Ketose reductase and aldose reductase were detected in germinating soybean axes, but not in cotyledons. Fructokinase and glucokinase were present in both axes and cotyledons. The data suggest a sorbitol pathway functioning in germinating soybean axes, which allows for the interconversion of glucose and fructose with sorbitol as an intermediate.     

The glucose transport system of the hyperthermophilic anaerobic bacterium Thermotoga neapolitana

The glucose transport system of the extremely thermophilic anaerobic bacterium Thermotoga neapolitana was studied with the nonmetabolizable glucose analog 2-deoxy-D-glucose (2-DOG). T. neapolitana accumulated 2-DOG against a concentration gradient in an intracellular free sugar pool that was exchangeable with external source of energy, such as pyruvate, and was inhibited by arsenate and gramicidin D. There was no phosphoenolpyruvate-dependent phosphorylation of glucose, 2-DOG, or fructose by cell extracts or toluene-treated cells, indicating the absence of a phosphoenolpyruvate:sugar phosphotransferase system. These data indicate that D-glucose is taken up by T. neapolitana via an active transport system that is energized by an ion gradient generated by ATP, derived from substrate-level phosphorylation.     

Substrate inhibition of maize endosperm sucrose synthase by fructose and its interaction with glucose inhibition

Sucrose synthase (EC 2.4.1.13) was purified to homogeneity from developing maize (Zea mays L.) endosperm. Substrate saturation and inhibitor kinetics were examined for the sucrose synthase reaction. The K_m-values for fructose and uridine diphosphate glucose (UDPGlc) were estimated to be 7.8 mM and 76 μM, respectively. Fructose concentrations over 20 mM inhibited sucrose synthase in an uncompetitive manner with respect to UDPGlc. Glucose was also found to be an uncompetitive inhibitor with respect to both fructose and UDPGlc. At inhibitory concentrations of fructose, the apparent K_i for glucose increased linearly with increasing fructose concentration. The results suggest an ordered kinetic mechanism for sucrose synthase where UDPGlc binds first and UDP dissociates last. Fructose and glucose both inhibit by binding to the enzyme-UDP complex. Fructose and glucose, which are present in maize endosperm as the products of invertase, could inhibit sucrose synthase, especially in basal regions of the kernel where hexosesmay accumulate.     

Differential sugar uptake by cell suspension cultures of <Emphasis Type="Italic">Rudgea jasminoides</Emphasis>, a tropical woody Rubiaceae

The primary utilization of carbohydrates by cell suspension cultures of Rudgea jasminoides, a native woody Rubiaceae from tropical forests, was investigated. Sucrose, glucose + fructose, glucose, or fructose were supplied as carbon sources. The growth curves of R. jasminoides cultured in glucose + fructose, glucose, or fructose showed similar patterns to that observed when sucrose was supplied to the cells, except that an increase in dry mass was observed at the beginning of the stationary growth phase in the media containing only one monosaccharide. The increase in hexose levels in the media during the early stages of the cultures indicated extracellular hydrolysis of sucrose, which was further supported by the increase in the activity of acid invertase bound to the cell wall. Glucose was preferentially taken up, whereas uptake of fructose was delayed until glucose was nearly depleted from the medium. Measurements of intracellular sucrose content and cytoplasmatic and vacuolar invertases indicate that the enzymatic activity seems to be correlated with a decrease in the hexose flux into the cells of R. jasminoides. Our results indicate that the behavior of cell suspension cultures of R. jasminoides regarding sugar utilization seems to be similar to other dicotyledonous undifferentiated cell suspension cultures.     

Dinitrophenol-induced efflux of sucrose from maize scutellum cells

Maize scutellum slices accumulated sucrose during incubation in glucose, fructose or sucrose. Sucrose was accumulated in two compartments, tentatively     

Influence of the carbon source on growth and rosmarinic acid production in suspension cultures of Coleus blumei

Suspension cultures of Coleus blumei were characterized with respect to growth and rosmarinic acid formation in media with different sugars and various sugar concentrations. Sucrose is the sugar with the highest stimulating effect on growth and rosmarinic acid accumulation, followed by glucose and fructose. The sugar alcohol mannitol cannot be metabolized by the plant cells. Sucrose is cleaved into glucose and fructose by the Coleus cells. Sucrose concentrations from 1 to 5% have an increasing positive effect on growth and rosmarinic acid synthesis in the cell cultures with a maximum rosmarinic acid content of 12% of the dry weight in medium with 5% sucrose; in medium with 6% sucrose rosmarinic acid accumulation obviously did not reach its highest level in the culture period of 14 days. A very high yield of rosmarinic acid (2 mg ml^-1 suspension) could also be achieved by maintaining a sucrose concentration of 2% during the whole culture period. The start of rosmarinic acid synthesis by the cell cultures seems to be regulated by the growth limitation when a nutrient, e.g. phosphate is depleted from the medium. The rate of rosmarinic acid accumulation is related to the amount of carbon left in the medium when growth ceases.Abbreviations RA rosmarinic acid     

Actinidia deliciosa in vitro II. Growth and exogenous carbohydrates utilization by explants

Changes in sugar composition (sucrose, glucose and fructose) of medium, callus, stem and leaves of in vitro proliferating explants of Actinidia deliciosa C.F. Liang, Hayward were analyzed together with explant growth at 0, 15, 30, 45 and 60 days of culturing. Autoclaving hydrolyzes a small part of the initial sucrose of the medium into glucose and fructose. In presence of Actinidia explants the initial sucrose decreased to 32% after 15 days of culturing, to 4% after 30 days and to 0.08% at the end of the culture period (60 days). Sucrose increase in the explants did not parallel with its decrease in the medium. Sucrose presence in the explants was evident only during the last month of culturing. After 15 days of culturing a large increase of glucose and fructose was found in the medium but it did not equal the hydrolyzed sucrose. The level of these two monosaccharides remained stable in the medium until the 30th day, then significantly decreased in the second month of culture; neither were completely exhausted at the end of the culture. In the whole explant the highest amount of glucose and fructose was reached after 30 days of culturing.The balance of the three sugars in the medium-explant system, as % distribution of carbon atoms, showed a utilization throughout the whole culture period.Qualitative analyses performed on medium, callus and leaves at 0, 15, and 30 days of culturing revealed the presence of glucose and fructose only and no significant amounts of other hexoses or pentoses. Starch accumulation in the leaves was also observed throughout the culturing.Paper No. 724     

Effect of acarbose on the increased plasma concentration of uric acid induced by sucrose ingestion

Sucrose is converted fructose and glucose, which may increase plasma uric acid concentration (pUA) through increased purine degradation and/or decreased uric acid (UA) excretion. To investigate effects of acarbose, an inhibitor of alpha-glucosidase, on the increased pUA from sucrose administration, we measured pUA and urinary UA excretion in 6 healthy subjects before and after administering sucrose, with and without co-administration of acarbose. Sucrose raised pUA by 10% (p < 0.01). However, excretion and fractional clearance of UA were unchanged. Sucrose and acarbose coadministration also increased pUA, but less than did sucrose alone (sucrose: 4.9 to 5.4 mg/dl; sucrose + acarbose, 4.7 to 4.9 mg/dl, p < 0.05) without changes in urinary excretion and fractional clearance of UA. Acarbose appears to attenuate the rise in pUA by sucrose ingestion by inhibiting sucrose absorption.     

Growth and energetics of Leuconostoc mesenteroides NRRL B-1299 during metabolism of various sugars and their consequences for dextransucrase production.

The metabolic and energetic properties of Leuconostoc mesenteroides have been examined with the goal of better understanding the parameters which affect dextransucrase activity and hence allowing the development of strategies for improved dextransucrase production. Glucose and fructose support equivalent specific growth rates (0.6 h-1) under aerobic conditions, but glucose leads to a better biomass yield in anaerobiosis. Both sugars are phosphorylated by specific hexokinases and catabolized through the heterofermentative phosphoketolase pathway. During sucrose-grown cultures, a large fraction of sucrose is converted outside the cell by dextransucrase into dextran and fructose and does not support growth. The other fraction enters the cell, where it is phosphorylated by an inducible sucrose phosphorylase and converted to glucose-6-phosphate (G-6-P) by a constitutive phosphoglucomutase and to heterofermentative products (lactate, acetate, and ethanol). Sucrose supports a higher growth rate (0.98 h-1) than the monosaccharides. When fructose is not consumed simultaneously with G-1-P, the biomass yield relative to ATP is high (16.8 mol of ATP.mol of sucrose-1), and dextransucrase production is directly proportional to growth. However, when the fructose moiety is used, a sink of energy is observed, and dextransucrase production is no longer correlated with growth. As a consequence, fructose catabolism must be avoided to improve the amount of dextransucrase synthesized.     

Sugar retrieval by coats of developing seeds of Phaseolus vulgaris L. and Vicia faba L

Influxes of glucose, fructose and sucrose were characterised for coat cells of developing seeds of Phaseolus vulgaris L. and Vicia faba L. by monitoring uptake of [(14)C]sugars into excised seed-coat halves and two different protoplast populations derived from seed coats. Sugar influxes by the two populations of protoplasts were similar for each sugar species [sucrose > (fructose approximately glucose)] and hexoses competed with sucrose. Concentration-dependent influxes of all three sugars by excised seed coats could be described by a simple directly proportional relationship between concentration ([S]) and uptake rate (v) in the physiological range of sugar concentrations (v approximately A.[S]). Alternatively, with the exception of fructose influx by Vicia, all could be fitted to a Michaelis-Menten relationship, as could sucrose uptake by Vicia protoplasts. Apparent K(m) values were high ( approximately 100-500 mM) compared with those reported for other systems. Sucrose transport was distinct from glucose and fructose transport in both species. Sugar influx was decreased by p-chloromercuribenzenesulfonic acid, carbonylcyanide m-chlorophenylhydrazone and erythrosin B. These responses are consistent with sugar/H(+) symport acting to retrieve photoassimilates leaked to the apoplasm during post-sieve element transport within seed coats.     

Insights into the fine architecture of the active site of chicory fructan 1-exohydrolase: 1-kestose as substrate vs sucrose as inhibitor

* Invertases and fructan exohydrolases (FEHs) fulfil important physiological functions in plants. Sucrose is the typical substrate for invertases and bacterial levansucrases but not for plant FEHs, which are usually inhibited by sucrose. * Here we report on complexes between chicory (Cichorium intybus) 1-FEH IIa with the substrate 1-kestose and the inhibitors sucrose, fructose and 2,5 dideoxy-2,5-imino-D-mannitol. Comparisons with other family GH32 and 68 enzyme-substrate complexes revealed that sucrose can bind as a substrate (invertase/levansucrase) or as an inhibitor (1-FEH IIa). * Sucrose acts as inhibitor because the O2 of the glucose moiety forms an H-linkage with the acid-base catalyst E201, inhibiting catalysis. By contrast, the homologous O3 of the internal fructose in the substrate 1-kestose forms an intramolecular H-linkage and does not interfere with the catalytic process. Mutagenesis showed that W82 and S101 are important for binding sucrose as inhibitor. * The physiological implications of the essential differences in the active sites of FEHs and invertases/levansucrases are discussed. Sucrose-inhibited FEHs show a K(i) (inhibition constant) well below physiological sucrose concentrations and could be rapidly activated under carbon deprivation.     

Modeling sucrose hydrolysis in dilute sulfuric acid solutions at pretreatment conditions for lignocellulosic biomass

Agricultural and herbaceous feedstocks may contain appreciable levels of sucrose. The goal of this study was to evaluate the survivability of sucrose and its hydrolysis products, fructose and glucose, during dilute sulfuric acid processing at conditions typically used to pretreat lignocellulose biomass. Solutions containing 25g/l sucrose with 0.1-2.0% (w/w) sulfuric acid concentrations were treated at temperatures of 160-200 degrees C for 3-12min. Sucrose was observed to completely hydrolyze at all treatment conditions. However, appreciable concentrations of fructose and glucose were detected and glucose was found to be significantly more stable than fructose. Different mathematical approaches were used to fit the kinetic parameters for acid-catalyzed thermal degradation of these sugars. Since both sugars may survive dilute acid pretreatment, they could provide an additional carbon source for production of ethanol and other bio-based products.