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At least 19 recordsLinked to original sources
PubMed1996

Purification and Characterization of the Enzymes of Fructan Biosynthesis in Tubers of Helianthus tuberosus Colombia (II. Purification of Sucrose:Sucrose 1-Fructosyltransferase and Reconstitution of Fructan Synthesis in Vitro with Purified Sucrose:Sucrose 1-Fructosyltransferase and Fructan:Fructan 1-Fructosyltransferase).

Sucrose:sucrose 1-fructosyltransferase (1-SST), an enzyme involved in fructan biosynthesis, was purified to homogeneity from tubers of Helianthus tuberosus that were harvested in the accumulation phase. Gel filtration under native conditions predicted a molecular mass of about 67 kD. Electrophoresis or gel filtration under denaturing conditions yielded a 27- and a 55-kD fragment. 1-SST preferentially catalyzed the conversion of sucrose into the trisaccharide 1-kestose (GF2). Other reactions catalyzed by 1-SST at a lower rate were self-transfructosylations with GF2 and 1,1-nystose (GF3) as substrates yielding GF3 and 1,1,1-fructosylnystose, respectively, as products. 1-SST also catalyzed the removal of the terminal fructosyl unit from both GF2 and GF3, which resulted in the release of sucrose and GF2, respectively, and free Fru. The purified enzyme did not display [beta]-fructosidase activity. An enzyme mixture of purified 1-SST and fructan:fructan 1-fructosyltransferase, both isolated from tubers, was able to synthesize fructans up to a degree of polymerization of at least 13 with sucrose as a sole substrate.

Journal Article↗
PubMed1991

Sucrose Phosphate Synthase, Sucrose Synthase, and Invertase Activities in Developing Fruit of Lycopersicon esculentum Mill. and the Sucrose Accumulating Lycopersicon hirsutum Humb. and Bonpl.

The green-fruited Lycopersicon hirsutum Humb. and Bonpl. accumulated sucrose to concentrations of about 118 micromoles per gram fresh weight during the final stages of development. In comparison, Lycopersicon esculentum Mill. cultivars contained less than 15 micromoles per gram fresh weight of sucrose at the ripe stage. Glucose and fructose levels remained relatively constant throughout development in L. hirsutum at 22 to 50 micromoles per gram fresh weight each. Starch content was low even at early stages of development, and declined further with development. Soluble acid invertase (EC 3.2. 1.26) activity declined concomitant with the rise in sucrose content. Acid invertase activity, which was solubilized in 1 molar NaCl (presumably cell-wall bound), remained constant throughout development (about 3 micromoles of reducing sugars (per gram fresh weight) per hour. Sucrose phosphate synthase (EC 2.4.1.14) activity was present at about 5 micromoles of sucrose (per gram fresh weight) per hour even at early stages of development, and increased sharply to about 40 micromoles of sucrose (per gram fresh weight) per hour at the final stages of development studied, parallel to the rise in sucrose content. In comparison, sucrose phosphate synthase activity in L. esculentum remained low throughout development. The possible roles of the sucrose metabolizing enzymes in determining sucrose accumulation are discussed.

Journal Article↗
PubMed1984

Comparison of sucrose-sucrose to sucrose-ethanol concurrent responding in the rat: reinforcement schedule and fluid concentration effects.

Rats maintained at 80% of their ad lib body weight were trained on a two bar concurrent fixed ratio 8-fixed ratio 8 schedule with sucrose solutions presented at schedule completion. When the solutions were available on the same schedule of reinforcement, rats consistently responded more on the lever associated with the higher sucrose concentration over either less concentrated sucrose solutions or water. However, when a preferred 20% sucrose solution was placed on a high fixed ratio requirement (FR64) and a less preferred 2% sucrose solution remained on the lower ratio requirement (FR8), the rats were observed to increase their responding on the lever associated with presentation of the 2% sucrose solution. Response rates for the low concentrated sucrose solution increased to levels comparable to those seen when that solution was paired with water. These results were compared to prior studies using ethanol and sucrose as the available fluids.

Animals↗
PubMed2005

Phloem-localized, proton-coupled sucrose carrier ZmSUT1 mediates sucrose efflux under the control of the sucrose gradient and the proton motive force.

The phloem network is as essential for plants as the vascular system is for humans. This network, assembled by nucleus- and vacuole-free interconnected living cells, represents a long distance transport pathway for nutrients and information. According to the Münch hypothesis, osmolytes such as sucrose generate the hydrostatic pressure that drives nutrient and water flow between the source and the sink phloem (Münch, E. (1930) Die Stoffbewegungen in der Pflanze, Gustav Fischer, Jena, Germany). Although proton-coupled sucrose carriers have been localized to the sieve tube and the companion cell plasma membrane of both source and sink tissues, knowledge of the molecular representatives and the mechanism of the sucrose phloem efflux is still scant. We expressed ZmSUT1, a maize sucrose/proton symporter, in Xenopus oocytes and studied the transport characteristics of the carrier by electrophysiological methods. Using the patch clamp techniques in the giant inside-out patch mode, we altered the chemical and electrochemical gradient across the sucrose carrier and analyzed the currents generated by the proton flux. Thereby we could show that ZmSUT1 is capable of mediating both the sucrose uptake into the phloem in mature leaves (source) as well as the desorption of sugar from the phloem vessels into heterotrophic tissues (sink). As predicted from a perfect molecular machine, the ZmSUT1-mediated sucrose-coupled proton current was reversible and depended on the direction of the sucrose and pH gradient as well as the membrane potential across the transporter.

Animals↗
PubMed1992

Sucrose Metabolism in Tubers of Potato (Solanum tuberosum L.): Effects of Sink Removal and Sucrose Flux on Sucrose-Degrading Enzymes.

Excision of developing potato (Solanum tuberosum L.) tubers from the mother plant, followed by storage at 10 degrees C, resulted in a rapid, substantial decrease in sucrose synthase activity and considerable increases in hexose content and acid invertase activity. A comparison of the response of three genotypes, known to accumulate different quantities of hexoses in storage, showed that both sucrose synthase activity and the extent to which activity declined following excision were similar in all cases. However, there was significant genotypic variation in the extent to which acid invertase activity developed, with tubers accumulating the highest hexose content also developing the highest extractable activity of invertase. Similar effects were found in nondetached tubers when growing plants were maintained in total darkness for a prolonged period. Furthermore, supplying sucrose to detached tubers through the cut stolon surface prevented the decline in sucrose synthase activity. Maltose proved to be ineffective. Western blots using antibodies raised against maize sucrose synthase showed that the decline in sucrose synthase activity was associated with the loss of protein rather than the effect of endogenous inhibitors. Although there were indications that maintaining a flux of sucrose into isolated tubers could prevent the increase in acid invertase activity, the results were not conclusive.

Journal Article↗
PubMed2005

Sucrose carrier RcSCR1 is involved in sucrose retrieval, but not in sucrose unloading in growing hypocotyls of Ricinus communis L.

The transport of assimilates from source to sink tissues is mediated by the phloem. Along the vascular system the phloem changes its physiological function from loading phloem to transport and unloading phloem. Sucrose carrier proteins have been identified in the transport phloem, but it is unclear whether the physiological role of these transporters is phloem unloading of sucrose or retrieval of apoplasmic sucrose back into the sieve element/companion cell complex. Here, we describe the dynamic expression of the Ricinus communis sucrose carrier RcSCR1 in the hypocotyl at different sink strengths. Our results indicate that phloem unloading in castor bean is not catalysed by the phloem loader RcSCR1. However, this sucrose carrier represents the molecular basis of the sucrose retrieval mechanism along the transport phloem, which is dynamically adjusted to the sink strength. As a consequence, we assume that other release carrier(s) exist in sink tissues, such as the hypocotyl, in R. communis.

Biological Transport, Active↗
PubMed1996

Sucrose metabolism during cotyledon development of Vicia faba L. is controlled by the concerted action of both sucrose-phosphate synthase and sucrose synthase: expression patterns, metabolic regulation and implications for seed development.

The roles of sucrose-phosphate synthase (Sps) and sucrose synthase (Sus) in developing embryos of Vicia faba have been characterized. In the cotyledons the expression of both Sps and Sus is initiated in cells differentiating into storage tissue. This stage is characterized by a switch in the carbohydrate state from a high to a low hexoses to sucrose ratio. The carbohydrate state was found earlier to be controlled by seed coat-associated invertase. During cotyledon development the Sps-enzyme undergoes a cycle of deactivation and reactivation: the activated state is associated with the prestorage phase, desiccation and germination and the deactivated state with the storage phase. Sus activity is associated with the storage phase. Sps and Sus are differentially influenced by free sugars. Feeding hexoses to storage phase cotyledons increases levels of Sps-mRNA but not Sus-mRNA, Sps activity and Sps activation state and impairs storage functions evidenced by an increased sucrose to starch ratio and a downregulation of storage protein legumin B-mRNA. Sus enzyme activity is inhibited by free hexoses in vitro. It is proposed that the changing carbohydrate state during cotyledon development controls the ratio of Sps to Sus. Sps may have some significance for the initiation of the storage process possibly decreasing hexoses and/or increasing sucrose. The relevance of the changing carbohydrate state with respect to development and storage processes is discussed.

Base Sequence↗
PubMed2002

Sucrose metabolism: Anabaena sucrose-phosphate synthase and sucrose-phosphate phosphatase define minimal functional domains shuffled during evolution.

Based on the functional characterization of sucrose biosynthesis related protiens[SBP: sucrose-phosphate synthase (SPS), sucrose-phosphate phosphatase (SPP), and sucrose synthase (SuS)] in Anabaena sp. PCC7120 and sequence analysis, we have shown that SBP are restricted to cyanobacterium species and plants, and that they are multidomain proteins with modular architecture. Anabaena SPS, a minimal catalytic SPS unit, defines a glucosyltransferase domain present in all SPSs and SuSs. Similarly, Anabaena SPP defines a phosphohydrolase domain characteristic of all SPPs and some SPSs. Phylogenetic analysis points towards the evolution of modern cyanobacterial and plant SBP from a bidomainal common ancestral SPS-like gene.

Anabaena↗
PubMed2004

The large subunit determines catalytic specificity of barley sucrose:fructan 6-fructosyltransferase and fescue sucrose:sucrose 1-fructosyltransferase.

Plant fructosyltransferases are highly homologous in primary sequence and typically consist of two subunits but catalyze widely different reactions. Using functional expression in the yeast Pichia pastoris, we show that the substrate specificity of festuca sucrose:sucrose 1--beta-D-fructosyltransferase (1-SST) and barley sucrose:fructan 6--beta-D-fructosyltransferase (6-SFT) is entirely determined by the large subunit. Chimeric enzymes with the large subunit of festuca 1-SST (LSuB) and the small subunit of barley 6-SFT have the same catalytic specificity as the native festuca 1-SST and vice versa. If the LSuB is expressed alone, it does not yield a functionally active enzyme, indicating that the small subunit is nevertheless essential.

Amino Acid Motifs↗
PubMed2002

Molecular characterization of sucrose:sucrose 1-fructosyltransferase and sucrose:fructan 6-fructosyltransferase associated with fructan accumulation in winter wheat during cold hardening.

We isolated two cDNAs of winter wheat (Triticum aestivum L.), designated wft1 and wft2, which encoded sucrose:fructan 6-fructosyltransferase (6-SFT) and sucrose:sucrose 1-fructosyltransferase (1-SST; EC 2.4.1.99), respectively, which are involved in the synthesis of fructan in wheat. wft1 and wft2 were cloned by screening of a cDNA library with probed-cDNA fragments corresponding to plant fructosyltransferase and invertase. The identity of the clones was verified by functional characterization of recombinant proteins expressed in methylotrophic yeast, Pichiapastoris. Northern blotting showed that the level of wft2 transcripts increased from autumn to early winter in the crown tissues of all field-grown wheat cultivars examined. Higher levels of wft1 and wft2 transcripts were found in leaf tissues of snow mold-resistant cultivars, which accumulated more fructan than other cultivars. Our results showed that Wft1 and Wft2 were important in fructan accumulation during cold hardening of winter wheat.

Amino Acid Sequence↗
PubMed2000

Sucrose for analgesia in newborn infants undergoing painful procedures.

BACKGROUND: Management of pain for neonates is less than optimal. The administration of sucrose with and without non-nutritive sucking (pacifiers) has been the most frequently studied non-pharmacological intervention for relief of procedural pain in neonates. OBJECTIVES: To determine the efficacy, effect of dose, and safety of sucrose for relieving procedural pain as assessed by physiologic and/or behavioural indicators. SEARCH STRATEGY: Standard methods as per the Neonatal Collaborative Review Group. A MEDLINE search was carried out for relevant randomized controlled trials (RCTs) published from January 1966 - November 1, 1997; EMBASE from 1993-1997; Reference Update search on November 11, 1997 and search of the Cochrane Library Issue 4 on November 11, 1997. Key words and (MeSH) terms included, infant/newborn, pain, analgesia and sucrose. Personal files, bibliographies, the most recent relevant neonatal and pain journals and conference proceedings were searched manually. Unpublished studies were not included. Language restrictions were not imposed. SELECTION CRITERIA: RCTs in which term and/or preterm neonates undergoing heel lance, venepuncture or intramuscular injection (immunization) received sucrose or water/placebo or no intervention. DATA COLLECTION AND ANALYSIS: Trial quality was assessed according to the methods of the Neonatal Collaborative Review Group. Quality measures included; blinding of randomization, blinding of intervention, completeness of follow up and blinding of outcome measurement. Data were abstracted and independently checked for accuracy by the two investigators. The inconsistency in outcome measures and differences in the statistical reporting of results made meta-analysis impossible. We were not able to identify two studies in which the same physiologic and/or behavioral outcomes following a noxious stimulus (heel-lance, venepuncture, intramuscular injection) were measured and reported in an identical fashion using means and standard deviations (or standard errors). The results are therefore reported for each accepted study separately. MAIN RESULTS: Fifteen studies were identified for possible inclusion in this systematic review. Five studies were excluded; three RCTs were excluded as in these trials the number of infants randomized to treatment vs. placebo groups were not reported; one study was not an RCT, and in one RCT the neonates did not undergo a painful procedure. Ten RCTs were included in this review. Sucrose in a wide range of dosages was generally found to decrease univariate physiologic (heart rate) and behavioural (the mean percent time crying, total cry duration, duration of first cry, and facial action) pain indicators and multivariate [Premature Infant Pain Profile (PIPP)] pain outcomes in neonates undergoing heelstick or venepuncture. An optimal dose of sucrose to reduce pain associated with procedures in preterm and term neonates could not be identified through this systematic review. REVIEWER'S CONCLUSIONS: Sucrose reduces physiologic and/or behavioral indicators of stress/pain in neonates following procedural pain stimuli (heel lance, venepuncture, immunization). There was inconsistency in the dose of sucrose that was effective and an optimal dose to be used in preterm and/or term infants could not be identified. Considerations for future research are to describe the painful procedure and intervention in detail, to use appropriate sample size to show a statistically significant reduction in pain, to use a multidimensional conceptualization of pain, to select outcome measures that are reliable and valid pain indicators and to account for the variation in the infant's response and context in which the pain is experienced. The use of repeated administrations of sucrose in neonates needs to be investigated. Use of sucrose in neonates that are very low birth weight, unstable and/or ventilated also needs to be addressed. (ABSTRACT TRUNCATED)

Analgesics↗
PubMed1995

Behavioral economics of concurrent ethanol-sucrose and sucrose reinforcement in the rat: effects of altering variable-ratio requirements.

These experiments examined the own-price and cross-price elasticities of a drug (ethanol mixed with 10% sucrose) and a nondrug (10% sucrose) reinforcer. Rats were presented with ethanol-sucrose and sucrose, both available on concurrent independent variable-ratio (VR) 8 schedules of reinforcement. In Experiment 1, the variable ratio for the ethanol mix was systematically raised to 10, 12, 14, 16, 20, and 30, while the variable ratio for sucrose remained at 8. Five of the 6 rats increased ethanol-reinforced responding at some of the increments and defended baseline levels of ethanol intake. However, the rats eventually ceased ethanol-reinforced responding at the highest variable ratios. Sucrose-reinforced responding was not systematically affected by the changes in variable ratio for ethanol mix. In Experiment 2, the variable ratio for sucrose was systematically increased while the ethanol-sucrose response requirement remained constant. The rats decreased sucrose-reinforced responding and increased ethanol-sucrose-reinforced responding, resulting in a two- to 10-fold increase in ethanol intake. Experiment 3 examined the substitutability of qualitatively identical reinforcers: 10% sucrose versus 10% sucrose. Increases in variable-ratio requirements at the preferred lever resulted in a switch in lever preference. Experiment 4 examined whether 10% ethanol mix substituted for 5% ethanol mix, with increasing variable-ratio requirements of the 5% ethanol. All rats eventually responded predominantly for the 10% ethanol mix, but total amount of ethanol consumed per session did not systematically change. In Experiment 5, the variable-ratio requirements for both ethanol and sucrose were simultaneously raised to VR 120; 7 of 8 rats increased ethanol-reinforced responding while decreasing sucrose-reinforced responding. These data suggest that, within this ethanol-induction procedure and within certain parameters, demand for ethanol-sucrose was relatively inelastic, and sucrose consumption was independent of ethanol-sucrose consumption. Demand for sucrose, on the other hand, was relatively elastic, and ethanol-sucrose readily substituted for it. The results are discussed in terms of applying a behavioral economic approach to relationships between drug and nondrug reinforcers.

Alcohol Drinking↗
PubMed1983

The effect of sucrose on the rate of de novo sucrose biosynthesis in leaf protoplasts from spinach, wheat and barley.

Protoplasts from the leaves of wheat, spinach, and barley were found to synthesize [14C]sucrose from 14CO2 at rates comparable with those of the parent tissue. CO2 fixation and sucrose biosynthesis ceased virtually immediately when the light was switched off. The effect of sucrose pretreatment on the rate of de novo sucrose biosynthesis was found to vary with leaf age and with plant species. Protoplasts from young wheat and spinach leaves showed an apparent stimulation of the rate of sucrose biosynthesis after sucrose pretreatment. In protoplasts from mature leaves of spinach, sucrose pretreatment produced inhibition. After sucrose pretreatment protoplasts from mature spinach leaves showed low rates of CO2 fixation, and sucrose biosynthesis compared with controls. Conversely, with protoplasts from mature leaves of wheat and barley, the rate of CO2 fixation was unchanged and there was little or no effect on the rate of sucrose biosynthesis after sucrose pretreatment. Preincubation with sucrose had no effect on the activity of sucrose-phosphate synthetase (EC 2.4.1.14), cytoplasmic fructose-1,6-bisphosphatase (EC 3.1.3.11), or UDPglucose pyrophosphorylase (EC 2.7.7.9) from spinach leaves. It was concluded that there is no direct feedback inhibition of sucrose on the sucrose biosynthetic pathway in leaves of spinach, wheat, and barley. The mechanism of inhibition of sucrose biosynthesis by sucrose in spinach remains to be elucidated.

Carbon Dioxide↗
PubMed1996

A soybean sucrose binding protein independently mediates nonsaturable sucrose uptake in yeast.

Heterologous expression of a cDNA encoding a 62-kD soybean sucrose binding protein in yeast demonstrates that this protein, independent of other plant proteins, mediates sucrose uptake across the plasma membrane. Sucrose binding protein-mediated sucrose uptake is nonsaturable up to 30 mM sucrose, is specific for sucrose, and is relatively insensitive to treatment with sulfhydryl-modifying reagents. Alteration of the external pH or pretreatment of the yeast cells with protonophores did not significantly affect the rate of 14C-sucrose uptake. This demonstrates that sucrose binding protein-mediated sucrose uptake is not dependent on H+ movement and delineates it from other plant sucrose transporters. Physiological characterization of sucrose uptake into higher plant cells has shown the presence of both saturable and nonsaturable uptake components. The nonsaturable mechanism is relatively insensitive to external pH, pretreatment with protonophores, and treatment with sulfhydryl-modifying reagents. Sucrose binding protein-mediated sucrose uptake in yeast mimics this physiologically described, but mechanistically undefined, nonsaturable sucrose uptake mechanism in higher plants. Functional characterization of the sucrose binding protein thus defines both a novel component of sucrose uptake and provides important insight into this nonsaturable sucrose uptake mechanism, which has remained enigmatic since its physiological description.

2,4-Dinitrophenol↗
PubMed1998

Cloning of sucrose:sucrose 1-fructosyltransferase from onion and synthesis of structurally defined fructan molecules from sucrose.

Sucrose (Suc):Suc 1-fructosyltransferase (1-SST) is the key enzyme in plant fructan biosynthesis, since it catalyzes de novo fructan synthesis from Suc. We have cloned 1-SST from onion (Allium cepa) by screening a cDNA library using acid invertase from tulip (Tulipa gesneriana) as a probe. Expression assays in tobacco (Nicotiana plumbaginifolia) protoplasts showed the formation of 1-kestose from Suc. In addition, an onion acid invertase clone was isolated from the same cDNA library. Protein extracts of tobacco protoplasts transformed with this clone showed extensive Suc-hydrolyzing activity. Conditions that induced fructan accumulation in onion leaves also induced 1-SST mRNA accumulation, whereas the acid invertase mRNA level decreased. Structurally different fructan molecules could be produced from Suc by a combined incubation of protein extract of protoplasts transformed with 1-SST and protein extract of protoplasts transformed with either the onion fructan:fructan 6G-fructosyltransferase or the barley Suc:fructan 6-fructosyltransferase.

Amino Acid Sequence↗
PubMed1990

Interaction of structural isomers of sucrose in the reaction between sucrose and glucosyltransferases from mutans streptococci.

Structural isomers of sucrose, i.e. disaccharides composed of glucose and fructose molecules with different glucosidic linkages, were examined for their effect on the reaction between sucrose and various glucosyltransferases (GTases) from Streptococcus mutans MT8148 and Streptococcus sobrinus 6715. Trehalulose (alpha 1-1), turanose (alpha 1-3), maltulose (alpha 1-4), and palatinose (alpha 1-6) were used as the sucrose analogues. Mutans streptococci were found not to utilize these sucrose analogues. Analysis of enzymatic products of GTase and sucrose with thin layer chromatography clearly revealed that glucan synthesis from [14C]sucrose by the various purified GTase preparations from S. mutans and S. sobrinus was inhibited in the presence of these sucrose analogues except turanose, resulting in the release of increased amounts of [14C]fructose and [14C]oligosaccharides. It was also found that the fructose residues in the oligosaccharides were derived from those of sucrose analogues but not sucrose itself. The Lineweaver-Burk plots of the substrate saturation kinetics of GTase vs sucrose indicated increased Km and Vmax in the presence of sucrose analogue, as compared with sucrose alone. Finally, these sucrose analogues except turanose inhibited sucrose dependent cellular adherence of S. sobrinus 6715 to a glass surface, while they scarcely inhibited the adherence of S. mutans MT8148. Among the analogues, maltulose appeared the most effective inhibitor against GTases in general.

Chromatography, Thin Layer↗
PubMed2004

Incubation of sucrose craving: effects of reduced training and sucrose pre-loading.

Time-dependent increases in cue-induced reward seeking after forced abstinence were described in rats with a history of cocaine or sucrose self-administration, suggesting reward craving incubates over time. In the present study, we examined the effects of reduced training experience, or sucrose pre-loading just prior to testing, on the incubation of sucrose craving. Sucrose seeking (responding in extinction and then for a sucrose-paired cue) increased over time in groups of rats that self-administered sucrose 6 h/day for 10 days and were tested at 1, 7, or 30 days of forced abstinence. We found that groups of rats that had self-administered 2 instead of 6 h/day showed a similar profile of responding. Incubation of sucrose craving was attenuated by free access to sucrose in home cages for 17 h immediately prior to testing assessed as extinction responding on days 1 and 30. However, this sucrose pre-loading had no effect on the time-dependent increase in responding for the sucrose-paired cue. In summary, reducing the training experience had no effect on the incubation of sucrose craving and free access to sucrose had only a limited effect-attenuating extinction responding. These results illustrate the strength of the incubation of craving and further suggest long-term changes in brain motivational circuitry following sucrose self-administration.

Analysis of Variance↗