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At least 19 recordsLinked to original sources
PubMed1976

Different proton-sugar stoichiometries for the uptake of glucose analogues by Chlorella vulgaris. Evidence for sugar-dependent proton uptake without concomitant sugar uptake by the proton-sugar symport system.

The uptake of hexoses by Chlorella vulgaris is accompanied by the uptake of protons. For 6-deoxyglucose a stoichiometry of one proton taken up per sugar molecule has been measured, whereas for 1-deoxyglucose approximately two protons are taken up per sugar molecule. It was found that in the presence of 1-deoxyglucose a considerable proportion of "carrier" catalyzes the transport of protons without the concomitant transport of sugar. Presumably, the binding of sugar initiates the translocation of the carrier-proton-sugar complex, but whereas 1-deoxyglucose can still dissociate from the complex at the external side of the cytoplasmic membrane, the translocation of the carrier-proton complex continues. This conclusion was reached since (a) the composition of the translocated carrier-proton-sugar complex is the same for both sugar. Its formation is a first order reaction with respect to protons. (b) When 6-deoxyglucose, present inside cells, is exchanged for external sugar, the exchange ratio is two to one when the external sugar is 1-deoxyglucose, two molecules of 6-deoxyglucose are lost for each molecule of 1-deoxyglucose entering. This result indicates that during uptake of 1-deoxyglucose statistically only each second carrier molecule appearing at the internal side of the cytoplasmic membrane is carrying sugar.

Binding Sites↗
PubMed1975

Simultaneous assay of neutral sugars and amino sugars by an automatic sugar analyzer: applications to glycoproteins.

The simultaneous assay of neutral sugars and amino sugars commonly found in glycoproteins is described. The automatic sugar analyzer used for the determination is based on the ion-exchange chromatography of sugar-borate complexes on a strong anion-exchange resin. The sugars are identified with the orcinol/sulfuric acid reagent. While less than 40 nmol of mannose, fucose, galactose, glucose, xylose, or arabinose is sufficient for analysis at least 200 nmol mannosamine, glucosamine, or galactosamine is required; acidic monosaccharides cannot be determined. The technique of sugar analysis is applied to structural studies on natural compounds, e.g. the monosaccharide composition of lichenan and the carbohydrate moiety of the glycoproteins ovomucoid and Collocalia mucoid.

Amino Sugars↗
PubMed1979

Location of the sugar-binding site of L-arabinose-binding protein. Sugar derivative syntheses, sugar binding specificity, and difference Fourier analyses.

The sugar-binding site of the L-arabinose-binding protein, an essential component of the high affinity L-arabinose uptake system in Escherchia coli, is located deep in a cleft formed by the asymmetric contributions from both of the two similar domains. The site was unambiguously identified with the electron-rich substrate analog 6-bromo-6-deoxy-D-galactose in a difference Fourier analysis. The observation that the original native structure might have been solved with bound L-arabinose necessitated the synthesis of a heavy atom analog, its structure consistent with the known sugar-binding specificity of the protein. Difference Fourier maps (3.5 A) of crystals soaked in 46 mM analog showed a peak 3.5 times background, which is attributed to the -CH2Br moiety of the analog. Superposition of a difference map onto a 2.8-A native electron density map indicated that the difference peak is 6 to 7 A from the reactive single cysteine (Cys-64) and partially coincident with an "extraneous" density found in the native map. This "extraneous" peak was previously attributed to a bound L-arabinose molecule, and its presence accounts for the early failures of difference Fourier analyses of crystals soaked in or co-crystallized with L-arabinose to locate the sugar-binding site.

Arabinose↗
PubMed1976

Sugar transport. Properties of mutant bacteria defective in proteins of the phosphoenolpyruvate: sugar phosphotransferase system.

The bacterial phosphotransferase system (PTS) catalyzes the transfer of the phosphoryl group from phosphoenolpyruvate to its sugar substrates, PTS sugars, concomitant with the translocation of these sugars across the bacterial membrane. The phosphorylation of a given sugar requires four proteins, two general proteins, Enzyme I, and the histidine-containing phosphocarrier protein of the PTS (HPr), used for all sugars, and a pair of proteins specific for that sugar, designated an Enzyme II complex. The phosphotransferase system has been implicated in regulating the induction of synthesis of some catabolic enzyme systems required for the utilization of sugars that are not substrates of the phosphotransferase system, and this and the accompanying reports are concerned with this phenomenon in Salmonell typhimurium and Escherichia coli. Mutants defective in Enzyme I (ptsI), HPr (ptsH), and certain Enzymes II were isolated, and their abilities to ferment and grow on a wide range of sugars and other compounds were determined. The mutants showed the expected properties on PTS sugars, but in addition, ptsH and tight ptsI mutants were unable to utilize certain non-PTS sugars, including maltose, melibiose, glycerol, glycerol-P, mannose-6-P, and, in E. coli, lactose. Leaky Enzyme I mutants could utilize these carbohydrates, but were unable to use them in the presence of a PTS sugar such as methyl alpha-D-glucopyranoside. In accord with the results reported by other laboratories, the inability of the mutants to utilize the non-PTS sugars was explained by the fact that these cells could not be normally induced to synthesize the corresponding catabolic enzyme systmes. This phenomenon is designated PTS-mediated repression. PTS-mediated repression was also observed in wild type cells, but by comparing wild type and leaky pts mutants it was shown that the sensitivity to repression by PTS sugars was greatest in mutants containing the lowest levels of Enzyme I or HPr. Furthermore, ptsI mutants containing a second site mutation in a gene for an Enzyme II were not repressed by the sugar substrate of that Enzyme II, although repression by other PTS sugars was not affected. Transport and other studies further indicated that neither appreciable uptake nor metabolism of the PTS sugars was required for these compounds to effect repression. The ptsH mutants showed the same phenotypic properties as the ptsI mutants with some important exceptions. First, they could ferment and grow on a PTS sugar, fructose. Second, after growth on fructose, (and to a lesser extent on glucose or mannose), such mutants were capable of utilizing other PTS sugars for a few generations. Third, growth of the ptsH mutants on fructose relieved PTS-mediated repression; after growth on fructose, but not on lactate, the mutants could grow for several generations on non-PTS sugars. Preliminary experiments indicated that growth on fructose resulted in the formation of one or more proteins that could substitute for HPr in the utilization of both PTS and non-PTS sugars.

Acetylglucosamine↗
PubMed1976

Sugar transport. 2nducer exclusion and regulation of the melibiose, maltose, glycerol, and lactose transport systems by the phosphoenolpyruvate:sugar phosphotransferase system.

The bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) can repress the synthesis of certain catabolic enzyme systems in Salmonelly typhimurium and Escherichia coli. The present studies are concerned with an explanation of PTS-mediated repression by studying induction of the catabolic systems required for utilization of the non-PTS sugars glycerol, maltose, melibiose, and lactose. Repression of synthesis of these enzyme systems by various concentrations of PTS sugars was studied in wild type cells, in pts mutants, and in pts crr double mutants described in the accompanying reports (Saier, M. H., Jr., Simoni, R. D., and Roseman, S (1976) J. Biol. Chem. 251, 6584-6597: Saier, M. H., Jr., and Roseman, S. (1976) J. Biol. Chem., 6598-6605). The extent of repression was found to correlate with the degree of inhibition of uptake of the inducing non-PTS sugars. In both uninduced cells and cells fully induced for the respective transport system listed above, PTS sugars inhibited these transport systems. With both induced and uninduced cell types pts mutants were much more sensitive than wild type cells, while pts crr double mutants were completely resistant to the effects of the PTS sugars. Kinetic studies with the fully induced cells indicated that inhibition of transport by PTS sugars was reversible, that it affected the Vmax rather than the Km of entry, and that PTS sugars did not inhibit the efflux of the non-PTS sugars. These and other results indicate that inhibition did not result from competition between the PTS and non-PTS sugars for the transport systems, nor to competition for metabolic energy. Inhibition appears to require interaction of the PTS sugar with its membrane-bound Enzyme II complex, but whether concomitant uptake and phosphorylation of trace quantities of the PTS sugars is also required remains to be determined.

Biological Transport, Active↗
PubMed2026

Genomic and functional characterization of sugar transporters reveals potential roles in sugar accumulation in a modern sugarcane cultivar.

Sugarcane (Saccharum spp.) is a globally important sugar crop whose productivity depends on efficient sugar transport from source to sink organs. However, systematic identification and functional characterization of sugar transporters (STs) in sugarcane cultivars remain limited. Here, we identified 190 non-redundant ST genes in sugarcane cultivar Guitang 42 (GT42) and phylogenetically classified them into nine groups within the Monosaccharide Transporter (MST), Sucrose Transporter (SUT), and Sugars Will Eventually be Exported Transporters (SWEET) families. Comparative evolutionary analysis revealed significant lineage-specific expansions in the PMT, STP subfamilies, and SWEET families compared to diploid and wild relatives, likely driven by polyploidization and intensive selection for sugar yield. Transcriptomic profiling across tissues and internode elongation stages demonstrated marked tissue-specific and developmental expression patterns. Yeast complementation assays confirmed the transport activity of candidate MSTs, SUTs and SWEETs, with confocal microscopy verifying their distinct subcellular localization at the plasma membrane, tonoplast, or endoplasmic reticulum. Furthermore, transient overexpression of several candidate transporters (ScSWEET4-T2, ScSWEET15, and ScTST4-T1) in Nicotiana benthamiana modulated soluble sugar accumulation, and their expression in sugarcane protoplasts activated key sugar-responsive marker genes (ScGPT2 and ScWIP4). Together, our study establishes a systematic genomic framework and identifies candidate functional transporters that govern sugar partitioning and storage, providing valuable genetic targets for molecular breeding and quality enhancement in sugarcane.

Functional characterization↗
PubMed1976

The concerted inactivation of Escherichia coli uridine diphosphate galactose 4-epimerase by sugar nucleotide together with a free sugar.

1. The combined effect of the sugar nucleotides UDP-D-fucose or UDP-D-glucuronic acid together with the free sugars D-fucose or L-arabinose is the inactivation of the Escherichia coli enzyme UDP-galactose 4-epimerase (EC 5.1.3.2). The sugar nucleotide or the free sugar alone or the sugar nucleotide plus 5'-Ump do not inactivate the enzyme. 2. The inactivation of the enzyme by its substrate UDP-D-glucose was not affected by the presence of free sugar. 3. In all cases the inactivation observed follows pseudo-first-order kinetics. 4. A comparison of various sugar nucleotides indicates that the hydroxymethyl group at position 6 of the sugar moiety of the natural substrates is important for substrate binding.

Arabinose↗
PubMed1977

Effect of sugars on salt reception in true slime mold Physarum polycephalum. Physicochemical interpretation of interaction between salt and sugar receptions.

Interaction between salt and sugar receptions in plasmodium of Physarum polycephalum was studied by using double-chamber method. Effect of sugars on salt reception was evaluated by measuring membrane potential and the motive force of tactic movement of the slime mold, where salt concentration in one compartment was increased successively with a fixed sugar concentration. Results are summarized as follows: (1) The presence of D-glucose, D-mannose, D-maltose, or sucrose in medium led to increase of the threshold concentration Cth, for salts (chlorides and nitrates of Li, Na, K), whereas D-ribose decreased the threshold for salt reception. D-galactose showed no appreciable effect on Cth of every salt species examined. No change in Cth for salt reception was observed until concentration of sugars exceeded their respective thresholds. (2) Double logarithmic plots of Cth for salts against sugar concentration followed different straight lines for different cations, whose slopes being closely correlated with the effects of lyotropic number of anions in the absence of sugars. (3) Plots of log Cth against the reciprocal of the absolute temperature, 1/T, gave linear relations, and the slopes of the straight line became small with increase of sugar concentration above their respective thresholds. Experimental results obtained here suggest that the structure of water at the interface of cell membrane plays an indispensable role in the interaction between salt and sugar receptions.

Anions↗
PubMed1978

Kinetic analyses of the sugar phosphate:sugar transphosphorylation reaction catalyzed by the glucose enzyme II complex of the bacterial phosphotransferase system.

The sugar phosphate:sugar transphosphorylation reaction catalyzed by the glucose Enzyme II complex of the phosphotransferase system has been analyzed kinetically. Initial rates of phosphoryl transfer from glucose-6-P to methyl alpha-glucopyranoside were determined with butanol/urea-extracted membranes from Salmonella typhimurium strains. The kinetic mechanism was shown to be Bi-Bi Sequential, indicating that the Enzyme II possesses nonoverlapping binding sites for sugar and sugar phosphate. Binding of the two substrates appears to occur in a positively cooperative fashion. A mutant with a defective glucose Enzyme II was isolated which transported methyl alpha-glucoside and glucose with reduced maximal velocities and higher Km values. In vitro kinetic studies of the transphosphorylation reaction catalyzed by the mutant enzyme showed a decrease in maximal velocity and increases in the Km values for both the sugar and sugar phosphate substrates. These results are consistent with the conclusion that a single Enzyme II complex catalyzes both transport and transphosphorylation of its sugar substrates.

Biological Transport↗
PubMed1975

[Studies on the various sugar-urea and sugar-starch-urea relationships with reference to the fermentation in the rumen and the digestibility of nutrients in fattening cattle].

Recommendations are given saying that sugar-to-crude fibre rations of not more than 1.7:1 and sugar-to-urea ratios of 12:1 should be used in the fattening of cattle fed urea-supplemented rations of roughages in which 40% to 50% of the crude protein content of the ration had been replaced by urea. The amount of sugar per kg live-weight should not exceed 4 g. Higher quantities reduce the digestibility of crude fibre and, additionally, decrease the NH3 level and the pH in the rumen. At the same time the amount of volatile fatty acids is increased while the content of ruminal acetic acid decreases. Variations in the sugar-to-starch ratio had no statistically significant influence on the nitrogen balance whereas it was found that increasing quantities of sugar significantly decreased the digestibility of crude fibre. The proportional content of sugar in the readily metabolisable carbohydrates contained in the ration should not exceed 20% to 50%.

Animal Feed↗
PubMed1976

Influence of specific dietary sugars on the jejunal mechanisms for glucose, galactose, and alpha-methyl glucoside absorption: evidence for multiple sugar carriers.

The effects of feeding glucose, galactose, and alpha-methyl glucoside on the kinetics of absorption of these sugars in the jejunum of the fasting rat were assessed by recently developed chemical and electrical methods for characterizing the electrogenic active transfer mechanisms in vivo. The parameters of 'apparent Km' (an index of carrier affinity) and Vmax (an index of the maximum jejunal transfer capacity) were obtained from the kinetic data to describe quantitatively the active transport mechanisms in rats fed their normal solid diet, in rats deprived of solid food for three days, and in rats deprived of solid food but allowed ad libitum access to isotonic solutions of glucose, galactose, or alpha-methyl glucoside for up to three days. Feeding the sugars to fasting rats produced complex differential effects on the 'apparent Km's' and Vmax's of the various transport mechanisms. The changes, although complex, can best be explained by alterations in the transport mechanisms per se rather than by non-specific changes in intestinal morphology or metabolism. The differential effects induced by the feeding sugars are further evidence for the concept that jejunal enterocytes possess multiple carriers or mechansims for the absorption of actively transported sugars in vivo. The multiple forms of the sugar carriers (isocarriers?) MAY BE INVOLVED IN THE FACULTATIVE RESPONSES OF THE ENTEROCYTES TO CHANGES IN THE DIETARY LEVELS OF SUGAR AND MAY BE IMPORTANT IN UNDERSTANDING THE INFLUENCES OF DISEASE AND NUTRITIONAL STATUS ON ABSORPTION PROCESSES IN MAN.

Animals↗
PubMed1976

Interrelationship between sugar-evoked increases in transmural potential difference and sugar influxes across the mucosal border in the small intestine.

The relationship between changes in the transmural potential induced by actively transported sugars(deltaPDs) and influxes of the sugars(Js's) was investigated in the isolated guinea pig small intestine. Under the condition that medium electrical conductivity. remains unchanged, deltaPD and Js were closely correlated, e.g., both showed very similar patterns of regional difference along the intestine, and the values of the half saturation concentration (Km) for a sugar estimated from electrical and flux measurements were nearly identical. No such correlation was observed when medium conductivity varied. However, a simple correction of the sizes of deltaPDs for medium conductivity restored a close parallelism between deltaPDs and Js's. The sugar-induced increase in Na+ flux estimated from the increase in short-circuit current varied in parallel with Js regardless of the medium conductivity, and a fixed stoichiometrical relationship (approximately one-to-one coupling) was seen between Na+ and sugar fluxes. It is concluded that the dominant factor affecting the interrelation between deltaPD and Js is the resistance of the paracellular shunt which is directly proportional to medium electrical conductivity

Animals↗
PubMedDate not supplied

Effect of sugar analogues on growth, sugar utilization, and acid production by Streptococcus mutans.

Studies on the effect of various structural analogues of glucose of phosphoenolpyruvate (PEP)-dependent sugar transport in Streptococcus mutans showed that sugars with alterations at carbon 2 were markedly inhibitory. Low concentrations of the nonfermentable analogue D-2-deoxyglucose (2-deoxyg) blocked the growth of S mutans in broth media containing various fermentable sugars. Acid production by S mutans from both exogenous glucose and intracellular storage polysaccharide was inhibited by 2-deoxyG. The analogue is bacteriostatic, and large quantities of intracellular 2-deoxyG-6-PO4 accumulate during exposure of S mutans to the sugar.

Animals↗
PubMed1978

High-performance liquid chromatographic investigation of the amino acid, amino sugar and neutral sugar content in glycoproteins.

A methods for the simultaneous separation and determination of amino acids, amino sugars and neutral carbohydrates is described. Stepwise elution systems with sodium citrate and borate buffers have developed for the ion-exchange liquid chromatographic separation of amino acids and sugars, using 8-micrometer particle size resins and the Stein and Moore and orcinol colorimetric method for detection. With the aid of this system, the direct quantitative comparison of sugars and amino acids by liquid chromatography becomes possible for the first time.

Amino Acids↗
PubMed1976

Sugars and sugar derivatives which inhibit the short-circuit current of the everted small intestine of the rat.

1. The short-circuit current of everted rat intestine supported on a perforated cannula proved to be stable for up to 3 hr and has been used to study competition between transportable and non-transportable sugars. 2. 4,6-O-Ethylidene-alpha-D-glucopyranose (ethylidene glucose) and 4,6-O-benzylidene-e alpha-D-glucopyranos (benzylinene glucose), two nontransportable inhibitors of the hexose transfer system in human erythrocytes, were found to reduce the short-circuit current generated by transportable sugars such as galactose or 3-O-methyl glucose. 3. These compounds were also found to reduce the basal short-circuit current established by the everted intestine in a sugar-free Krebs solution. Both types of inhibition approached saturation at the higher concentrations used. 4. Similar inhibitory properties were shown by mannose, a non-actively accumulated monosaccharide, and by the beta-disaccharides lactose and cellobiose. 5. It is suggested that this common pattern of behaviour is due to the ability of these compounds to react with the sites for active hexose transfer but without translocation by the system. The significance of the inhibition of the basal short-circuit current is briefly discussed in this context.

Animals↗
PubMed1977

Photochemical conversion of sugar dimethylthiocarbamates into deoxy sugars.

Protected sugar derivatives having one free hydroxyl group may be deoxygenated at the alcoholic position by ultraviolet irradiation of the corresponding dimethylthiocarbamic esters; a concomitant process leads also to the original alcohol. Thus, on photolysis, the 6-dimethylthiocarbamate (1) of 1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose (3) gives 6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose (2) together with 3. Likewise, the 4-dimethylthiocarbamate (6) of 1,6-anhydro-2,3-O-isopropylidene-beta-D-mannopyranose (8) gives a mixture of the 4-deoxy derivative 7 and the alcohol 8. 3-Deoxy-1,2:5,6-di-O-isopropylidene-alpha-D-ribo-hexofuranose (10) was obtained by irradiation of 3-O-(dimethylthiocarbamoyl)-1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose (9), and was accompanied by 1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose (11). The 3-deoxy-3-iodo analog (14) of 11 underwent conversion into 10 by photolysis, and the deoxy sugar 10 was also prepared from 3,3'-dithiobis(1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose) (12) by the action of Raney nickel. Photolysis of the 2-dimethylthiocarbamate (16) of methyl 3,4-O-isopropylidene-beta-L-arabinopyranoside (18 gave the 2-deoxy derivative (17), together with the parent alcohol 18, and the same pair of products was obtained by the action of tributylstannane on the 2-(methylthio)thiocarbonyl derivative (19) of 18, although the dimethylthiocarbamate 16 was unreactive toward tributylstannane.

Arabinose↗