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PubMed2004

Changes in sugar content and activity of vacuolar acid invertase during low-temperature storage of potato tubers from six Japanese cultivars.

The storage of potato tubers at low temperatures leads to the accumulation of sugars in a process called "low-temperature sweetening." To understand this phenomenon, we measured the sugar contents and the activity of acid invertase over several months in tubers of six Japanese cultivars stored at 4 degrees C or 20 degrees C. At 20 degrees C, few changes in sugar contents took place in any of the tubers. On the other hand, when stored at 4 degrees C, three types of changes were observed among the cultivars: (1) increased levels of reducing sugars during storage; (2) a pattern similar to that of type 1, but with 4- to 6-fold lower levels of reducing sugars throughout storage; and (3) increased sucrose, but not reducing sugars. The activity of vacuolar acid invertase increased in the type-1 cultivars, whereas, in the type-2 and type-3 cultivars, the activities were very low during storage at 4 degrees C. Reverse transcription-polymerase chain reaction analysis of acid invertase showed that the transcripts of the enzyme accumulated in the tubers stored at 4 degrees C in the type-1 cultivars but not in type-3. These results suggest that the activity of vacuolar acid invertase is related to the types of changes that occurred in sugar content during low-temperature storage among the potato cultivars.

Cold Temperature↗

PubMed1982

In vivo and in vitro sugar transport in frog intestine.

In the frog intestine, both in vitro and in vivo, experiments were carried out in order to increase knowledge of the mechanism of sugar exit across the basolateral membrane of the enterocyte. The frog intestine was chosen because it lacks crypt cells and, consequently, any external fluid circuit mechanism during sugar transport can be avoided. Therefore, the sugar concentration in the absorbate collected on the serosal side is likely to be similar to that present underneath the basolateral membrane of the enterocyte. Under this condition, cell and absorbate sugar concentrations are similar; yet there is a concomitant net transintestinal sugar transport. Moreover, in in vivo experiments a net transintestinal sugar transport takes place even against a concentration difference. These results suggest that sugar exit across the basolateral membrane is not simply due to a chemically facilitated diffusion.

3-O-Methylglucose↗

PubMed1993

The effect of sugars on the morphology of the bacterial flagellum.

Using dark-field microscopy, we have found that certain sugars cause the normal-to-curly helical transition of bacterial flagella. Titration of flagella isolated from Salmonella typhimurium with 16 different carbohydrates showed that: (i) only certain sugars cause the transition. There is no obvious relationship between the simple physico-chemical properties of the sugar and whether the sugar causes the transition or not; (ii) the efficacies of sugars that do cause the transition differ markedly. For these sugars there is a relationship between efficacy and molecular size. These results suggest that the specific, though weak, binding of sugars to sites on flagella cause the morphological transition.

Carbohydrate Conformation↗

PubMed1986

Effects of diets high in simple sugars on urinary chromium losses.

Thirty-seven subjects, 19 men and 18 women, consumed reference diets for 12 weeks formulated by nutritionists to contain optimal levels of protein, fat, carbohydrate, and other nutrients; the following 6 weeks, subjects consumed high sugar diets. The reference diets contained 35% of total calories from complex carbohydrates and 15% from simple sugars while the high sugar diets contained 15% complex carbohydrates and 35% simple sugars. Chromium contents of the reference and high sugar diets were both approximately 16 micrograms per 1000 calories. Compared to the reference diets, consumption of the high sugar diets increased urinary Cr losses from 10% to 300% for 27 of 37 subjects. Urinary Cr excretion of males and females was similar, and there was no significant difference in Cr absorption (calculated from urinary excretion divided by intake times 100) between sexes when adjusted for the increased caloric intake of males. These data demonstrate that consumption of diets high in simple sugars stimulates Cr losses; this coupled with marginal intake of dietary Cr may lead to marginal Cr deficiency, which is associated with impaired glucose and lipid metabolism.

Adult↗

PubMed1988

Lactic acid bacteria: model systems for in vivo studies of sugar transport and metabolism in gram-positive organisms.

Lactic acid bacteria provide a model system for the in vivo study of mechanisms pertaining to the regulation of sugar transport and metabolism by microorganisms. Recent studies with resting and growing cells of the homofermentative Streptococci and Lactobacilli have yielded evidence for hitherto unsuspected regulatory mechanisms in this group of industrial and medically important bacteria. These regulatory mechanisms mediate the exclusion and expulsion of sugars, the preferential transport of sugar from sugar mixtures, resistance to non-metabolizable sugar analogs and participate in the establishment of energy-dissipating futile cycles. Transport experiments conducted with novel sugar analogs, data from enzymatic analyses and 31P-NMR spectroscopy studies with wild type and mutant strains of Streptococci, have provided new insight into the fine- and coarse-controls responsible for the modulation of activity of the sugar transport: glycolysis cycle. The purpose of this review is to summarize our current knowledge of these regulatory mechanisms and to suggest avenues for future investigation. Although specifically addressed to the lactic acid bacteria, it seems likely that some of the mechanisms described will be found in other Gram-positive species.

Biological Transport↗

PubMed1983

Stimulatory and inhibitory effects of hydrogen peroxide, diamide and vitamin K-5 on sugar transport in rat soleus muscle.

The experiments examined the stimulatory effects of H2O2, diamide and vitamin K-5 on the uptake of D-[U-14C]xylose by rat soleus muscle. All three oxidants stimulated sugar transport to the same extent, which was 30-40% of the maximal stimulatory effect of insulin (0.1 U/ml). Maximum stimulation was achieved with vitamin K-5 (0.01-0.1 mM), diamide (0.3 mM) and H2O2 (5-10 mM); at these concentrations the oxidants did not affect muscle ATP levels. Cytochalasin B (5 microM) abolished oxidant-stimulated xylose uptake. Catalase (20 U/ml) abolished the stimulatory effect of H2O2, but did not affect diamide- or vitamin K-5-stimulated transport. The ability of oxidants to stimulate sugar transport in anaerobic muscle could be demonstrated in short term (30 min) experiments, where muscle contained about 50% of its original ATP, but not after 120 min, when ATP levels were depleted. Oxidant-stimulated sugar transport was diminished and even abolished at supra-optimal oxidant concentrations; at these higher concentrations muscle ATP levels were lowered. All three oxidants inhibited the stimulatory effect of 2,4-dinitrophenol on sugar transport; this effect could be demonstrated using those oxidant concentrations which induced maximal stimulation of basal xylose uptake and which did not affect muscle ATP. It is concluded that: (1) H2O2, diamide and vitamin K-5 stimulate stereospecific sugar transport in soleus muscle by some mechanism other than lowering of ATP levels; (2) stimulation of sugar transport by oxidants is an ATP-dependent process; (3) some oxidant-sensitive sulphydryl group is critically involved in the process which activates muscle sugar transport.

Adenosine Triphosphate↗

PubMed2004

Preservation of dried liposomes in the presence of sugar and phosphate.

It has been well established that sugars can be used to stabilize liposomes during drying by a mechanism that involves the formation of a glassy state by the sugars as well as by a direct interaction between the sugar and the phospholipid head groups. We have investigated the protective effect of phosphate on solute retention and storage stability of egg phosphatidylcholine (egg PC) liposomes that were dried (air-dried and freeze-dried) in the presence of sugars and phosphate. The protective effect of phosphate was tested using both glucose (low T(g)) and sucrose (high T(g)) by measuring leakage of carboxyfluorescein (CF), which was incorporated inside the vesicles. Liposomes that were dried with glucose or phosphate alone showed complete leakage after rehydration. However, approximately 30% CF-retention was obtained using mixtures of phosphate and glucose. Approximately 75% CF-retention was observed with liposomes that were dried with sucrose. The solute retention further increased to 85% using mixtures of phosphate and sucrose. The pH of the phosphate buffer prior to drying was found to have a strong effect on the solute retention. Fourier transform infrared spectroscopy studies showed that phosphate and sugars form a strong hydrogen bonding network, which dramatically increased the T(g). The HPO(4)(2-) form of phosphate was found to interact stronger with sugars than the H(2)PO(4)(-) form. The increased solute retention of liposomes dried in the sugar phosphate mixtures did not coincide with improved storage stability. At temperatures below 60 degrees C the rate of solute-leakage was found to be strikingly higher in the presence of phosphate, indicating that phosphate impairs storage stability of dried liposomes.

Carbohydrates↗

PubMed2005

Combined sugar yields for dilute sulfuric acid pretreatment of corn stover followed by enzymatic hydrolysis of the remaining solids.

A number of previous studies determined dilute acid pretreatment conditions that maximize xylose yields from pretreatment or glucose yields from subsequent digestion of the pretreated cellulose, but our emphasis was on identifying conditions to realize the highest yields of both sugars from both stages. Thus, individual xylose and glucose yields are reported as a percentage of the total potential yield of both sugars over a range of sulfuric acid concentrations of 0.22%, 0.49% and 0.98% w/w at 140, 160, 180 and 200 degrees C. Up to 15% of the total potential sugar in the substrate could be released as glucose during pretreatment and between 15% and 90+% of the xylose remaining in the solid residue could be recovered in subsequent enzymatic hydrolysis, depending on the enzyme loading. Glucose yields increased from as high as 56% of total maximum potential glucose plus xylose for just enzymatic digestion to 60% when glucose released in pretreatment was included. Xylose yields similarly increased from as high as 34% of total potential sugars for pretreatment alone to between 35% and 37% when credit was taken for xylose released in digestion. Yields were shown to be much lower if no acid was used. Conditions that maximized individual sugar yields were often not the same as those that maximized total sugar yields, demonstrating the importance of clearly defining pretreatment goals when optimizing the process. Overall, up to about 92.5% of the total sugars originally available in the corn stover used could be recovered for coupled dilute acid pretreatment and enzymatic hydrolysis. These results also suggest that enhanced hemicellulase activity could further improve xylose yields, particularly for low cellulase loadings.

Catalysis↗

PubMed2006

Readiness to change sugar sweetened beverage intake among college students.

The prevalence of obesity is a topic of concern in the United States, especially among children and young adults, and there is also a growing concern that sugared beverage consumption may contribute to increasing obesity rates. However, few studies to date have examined sugar sweetened beverage consumption trends in college students. This study investigated self-reported sugared beverage consumption, nutritional knowledge, and readiness to change sugar sweetened beverage intake in college students (N=201; 33% minority). On average, non-overweight students reported significantly greater intake of sugared beverages than overweight students, and minority students reported greater consumption than Caucasians. A substantial majority of the sample (69%) reported that they had recently reduced their intake or were maintaining a reduction in intake. However, even those students indicating reduction in consumption reported intake of at least one sugar sweetened beverage daily. This suggests that high calorie beverage intake is a significant concern among young adult college-aged populations and that interventions targeting excess sugar sweetened beverage intake may have a role in obesity prevention efforts for this population.

Adolescent↗

PubMed2006

Effect of ammonium concentration on alcoholic fermentation kinetics by wine yeasts for high sugar content.

Kinetics of alcoholic fermentation by Saccharomyces cerevisiae wine strains in a synthetic medium with high sugar content were established for different nitrogen initial content and are presented for four strains. The composition of the medium was close to grape must except that the nitrogen source consisted mainly in ammonium and was varied from 120 to 290 mg N/l assimilable nitrogen. The overall nitrogen consumed was also estimated in order to determine nitrogen requirement variability. The effect of assimilable nitrogen was in general greater on sugar consumption rates than on growth and three kinds of effect on sugar consumption rates were observed: (i) existence of an optimal initial nitrogen level for a maximal sugar consumption rate (inhibition if excess), (ii) no effect of nitrogen beyond the intermediary level (saturation), (iii) sugar consumption rate proportional to the initial nitrogen level (activation). In all cases, the amount of consumed nitrogen increased with its initial concentration and so did the fructophilic capacity of the strains. The optimal requirement varied from 0.62 to 0.91 mg N/g of sugars according to different strains. There was no general correlation between the sugar assimilation rates and the nitrogen requirement.

Biomass↗

PubMed2005

Adverse effect of high added sugar consumption on dietary intake in American preschoolers.

OBJECTIVES: To assess the effect of Dietary Reference Intakes (DRI)-recommended added sugar intake levels on nutrient and food group consumption by preschoolers. STUDY DESIGN: This was a cross-sectional study of 2- to 5-year-olds in the United States Department of Agriculture Continuing Survey of Food Intake by Individuals (CSFII), 1994 to 1996, and 1998 (n = 5437). Main food sources of added sugar were established. For five categories (< or =10% energy from added sugar, 11% to 15%, 16% to 20%, 21% to 25%, and >25%), mean nutrient and food group consumption and proportion of children not meeting the DRI were ascertained. The nonparametric test for trend indicated significance of changes. Analysis was stratified by age (2- to 3-year-olds versus 4- to 5-year-olds), and survey design corrected to maintain the nationally representative character of the data. RESULTS: The majority of children consumed less than 25% of energy from added sugar; the main sources were fruit and or soft drinks and desserts. Increasing added sugar consumption was paralleled by decreasing nutrient and food group intakes and increasing proportions of children with intakes below the DRI. Calcium intake was insufficient in large proportions of children consuming 16% or more from added sugar. CONCLUSIONS: In preschoolers, the new DRI for added sugar are reason for concern. Further research is needed to investigate the effects of the DRI on diet quality, body weight, and health status in young children.

Child Nutritional Physiological Phenomena↗

PubMed2006

Changes in the pool of soluble sugars induced by dehydration at the heterotrophic phase of growth of wheat seedlings.

Loss of dehydration tolerance coincides with a shift from heterotrophy to autotrophy during post-germination growth of spring wheat seedlings. This critical stage falls on the fifth day following imbibition. Till the sixth day of experiment light had no effect on dry weight of the seedlings but the survival of six day old seedlings was reduced by half upon dehydration. Germinating seeds in the presence of 5 mM glucose, fructose, mannose or sucrose did not promote seedling growth but either increase (glucose, fructose) or decreased (mannose, sucrose) the survival of dehydrated seedlings. Protection against dehydration by the former sugars was correlated, irrespective of the seedling age, with the decrease of sugar pool in seeds and increase in shoots (coleoptile and first leaf) and roots. The opposite changes were provoked by the sugars hampering seedling survival. Generally, survival of wheat seedlings was not correlated with the size of soluble sugar pool but its distribution and composition. Lower mobilisation of soluble sugars in seed, lower proportion of reduced sugars to sucrose and higher share of raffinose is characteristic for the tolerant four day old seedlings and those grown in the media containing glucose or fructose. The results presented indicate that higher proportion of reduced sugars to sucrose and lower share of raffinose in six day old seedlings seems to be associated with the loss of dehydration tolerance of these seedlings, despite heterotrophic character of growth.

Carbohydrates↗

PubMed2004

EPR and UV spectral study of gamma-irradiated white and burned sugar, fructose and glucose.

The EPR and UV spectral properties of gamma-irradiated white and burned sugar, fructose and glucose are studied with the accent on their suitability as dosimetric materials. It is shown that gamma-irradiation of solid samples of white sugar and fructose yields stable EPR spectra whereas glucose signal remains time-dependent even 11 months later. Sugar and glucose exhibit linear EPR dose response in the region 0.44-21 kGy and fructose only up to ca. 10 kGy. The relative radiation sensitivity obtained for sugar and fructose is up to 10 kGy and slightly lower for glucose. Burned saccharides provide 2-3 orders of magnitude lower EPR radiation sensitivity making them not suitable for the proposed designation. According to the UV spectra water solutions of gamma-irradiated solid white saccharides show well pronounced absorption bands at 267 and 286 nm for sugar and fructose with time-dependent intensities reaching steady values ca. 11 days after dissolution. The intensities of these absorption bands are in linear relation with the absorbed dose of gamma-radiation. Glucose shows low sensitively because irradiation with 5.5 kGy yields only a shoulder at about 260-280 nm with decreasing to ca. 40% intensity in the first few days after dissolution. Excellent correlation between the intensities of the EPR- and UV-absorbed dose response is found for sugar and fructose in the region 0.44-10 kGy. This opens new possibilities for independent calibration the EPR dose response. Finally, the comparison suggests sugar as the best, universal material for EPR- and/or UV-dosimetry in the region 0.44-160 kGy.

Carbohydrates↗

PubMed2004

Re-cycling of sugar-ash: a raw feed material for rotary kilns.

Large amounts of sugar-ash, a material rich in calcium carbonate, are produced as a by-product in the Greek Sugar Industry. This work explores the possibility of re-cycling sugar-ash for use in the lime industry. A representative sample of sugar-ash from the Plati Imathias sugar plant was studied by PXRD, TG/DTG, calcination experiments at temperatures between 650 and 1150 degrees C and experiments to determine the quality of the quicklime produced at temperatures between 850 and 1150 degrees C following methods described in ASTM C110 standard. The sugar-ash was found to consist of 90 wt% calcium rich minerals (calcite and monohydrocalcite) and 10 wt% amorphous material. Traces of quartz were also detected. The quicklime of highest quality was produced at 950 degrees C. It is concluded that this "useless" material (sugar-ash) can be re-cycled for use in rotary kilns in the lime industry at calcination temperatures up to 950-1000 degrees C.

Calcium Compounds↗

PubMed2000

Effects of vitrified and nonvitrified sugars on phosphatidylcholine fluid-to-gel phase transitions.

DSC was used to study the ability of glass-forming sugars to affect the gel-to-fluid phase transition temperature, T(m), of several phosphatidylcholines during dehydration. In the absence of sugars, T(m) increased as the lipid dried. Sugars diminished this increase, an effect we explain using the osmotic and volumetric properties of sugars. Sugars vitrifying around fluid phase lipids lowered T(m) below the transition temperature of the fully hydrated lipid, T(o). The extent to which T(m) was lowered below T(o) ranged from 12 degrees to 57 degrees, depending on the lipids' acyl chain composition. Sugars vitrifying around gel phase lipids raised T(m) during the first heating scan in the calorimeter, then lowered it below T(o) in subsequent scans of the sample. Ultrasound measurements of the mechanical properties of a typical sugar-glass indicate that it is sufficiently rigid to hinder the lipid gel-to-fluid transition. The effects of vitrification on T(m) are explained using the two-dimensional Clausius-Clapeyron equation to model the mechanical stress in the lipid bilayer imposed by the glassy matrix. Dextran and polyvinylpyrrolidone (PVP) also vitrified but did not depress T(m) during drying. Hydration data suggest that the large molecular volumes of these polymers caused their exclusion from the interbilayer space during drying.

Biophysical Phenomena↗

PubMed1985

Measurement of neutral sugars in glycoproteins as dansyl derivatives by automated high-performance liquid chromatography.

Automated high-performance liquid chromatography was used to analyse dansylhydrazine derivatives of neutral sugars in unfractionated acid hydrolysates of four well-characterized glycoproteins: fetuin, ovalbumin, alpha-1-acid glycoprotein and bovine submaxillary mucin. After a simple single-step derivatization at 65 degrees C the sugar derivatives in protein hydrolysates chromatographed as single peaks on reversed-phase C18 columns. The isocratic solvent consisted of 20% (v/v) aqueous acetonitrile containing 0.01 M formic acid, 0.04 M acetic acid and 0.001 M triethylamine. The triethylamine significantly increases the sugar peak height at 254 nm. Repeated automatic sample injection without deterioration of column performance or interference from dansyl hydrazine is not possible with published methods, but was achieved by cleaning the column between each analysis with a solvent of 20% (v/v) acetonitrile and 80% (v/v) methanol. Hydrolysis with 2 M trifluoroacetic acid is superior to 2 M hydrochloric acid for both sugar recovery and convenience but must continue for 6-8 h at 105 degrees C to ensure complete sugar release. We confirmed that mannose is present in most preparations of human high-molecular-weight salivary glycoproteins, and also examined purified bovine skin proteodermatan sulphate. p-Nitrophenylhydrazine derivatives of neutral sugars are readily produced, but do not chromatograph as successfully as the dansyl derivatives while phenylhydrazine derivatives are not easily produced at 65 degrees C. Further development of the method should be possible by producing other hydrazine derivatives of neutral sugars.

Autoanalysis↗

PubMed2002

Triterpenoid saponins stimulate the sugar taste receptor cell through a G protein-mediated mechanism in the blowfly, Phormia regina.

The blowfly has taste chemosensilla on the labellum. The sensory receptor cells in the chemosensillum are highly specialized for the tastes of sugar, salt and water, respectively. Previously we introduced chromosaponin I (CSI) and glycyrrhizin (GL), as sweet substances for the blowfly, Phormia regina. Application of these triterpenoid saponins induced feeding responses as well as impulses of the sugar taste receptor cell in the LL-type sensillum at a much lower concentration than that of sucrose. In the present paper, we show the involvement of G protein-mediated cascade in the CSI- and GL-responses as well as in sugar responses. CSI activates the sugar signal transduction cascade after penetrating through the membrane. On the other hand, GL exerts dual effects to stimulate the sugar signal transduction possibly by activating it inside the cell and also by interacting with the pyranose sugar receptor site. A non hydrolyzable G protein inhibitor guanosine 5'-O-(2-thiodiphosphate), GDPbetaS, markedly decreased the responses of the sugar receptor cell to the two triterpenoid saponins as well as the response to sucrose and fructose. These results suggest that CSI and GL are direct activators of G protein.

Journal Article↗

PubMed2000

Sugar sensing and Ca2+-calmodulin requirement in Vitis vinifera cells producing anthocyanins.

We have previously reported that sucrose modulates anthocyanin biosynthesis in cell suspension cultures of Vitis vinifera L. The main role of sugar in this response does not seem to be that of general carbohydrate source for the supply of energy. In the present work, a number of pharmacological agents were used to further investigate the components of the signal transduction pathway involved in the induction of anthocyanin biosynthesis by sugar. We found that the phosphorylation of hexose by hexokinase, but not its transport, has to be taken into account for the sucrose signal transduction leading to anthocyanin accumulation. Indeed, 3-O-methylglucose, a glucose analog transported into cells but not phosphorylated by hexokinase, has no effect on anthocyanin production. Mannose mimics the effect of sucrose in grape cells, and mannoheptulose, a specific inhibitor of hexokinase, reduces the accumulation of anthocyanins in response to sucrose. The results with the two latter analogs are discussed. Ca2+ channel blockers, verapamil and LaCl3, which were used to investigate the role of extracellular Ca2+, all inhibited the sugar response. Ca2+ depletion by pretreatment with ethylene glycol bis (beta-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) also blocked the sugar response, which was partially recovered when Ca2+ was added exogenously after Ca2+ depletion. The use of two potent calmodulin antagonists, N-(6-aminohexyl)-5-chloro-1-naphtalenesulphonamide (W7) and chlorpromazine, showed that calmodulin is involved in the sugar signal transduction. A protein kinase inhibitor, 6-dimethylaminopurine (6-DMAP), and the protein phosphatase inhibitors, endothall and cantharidin, also inhibited the sugar response. The results of the present study suggest the involvement of several components of general signal transduction pathways such as Ca2+, calmodulin, and protein kinases phosphatases in the induction of anthocyanin biosynthesis by sugar.

Anthocyanins↗