Showing papers on "Disaccharide published in 1989"

Physiological Basis and Ecological Consequences of Sugar Preferences in Cedar Waxwings

Abstract: -In paired preference tests Cedar Waxwings (Bombycilla cedrorum) preferred glucose, fructose, and a mixture of glucose and fructose over sucrose. Preferences for simple sugars were ranked as: glucose = glucose + fructose > fructose > sucrose. To be absorbed by the brush border membrane, sucrose is hydrolyzed into its monosaccharide components, glucose and fructose. Because Cedar Waxwings preferred glucose and fructose over sucrose, we predicted that they would be sucrase deficient. We tested this by measuring the efficiency with which Cedar Waxwings absorbed glucose, fructose, and sucrose in vivo, and by directly assaying for sucrase in preparations of intestinal mucosa. Absorption efficiencies measured using a double isotope method falsified our prediction. Cedar Waxwings were able to absorb sucrose (absorption efficiency = 61% ? 1.2), but absorbed glucose and fructose more efficiently (absorption efficiencies = 92%? 1.5 and 88%?3.5, respectively). The presence of sucrase activity in Cedar Waxwings was confirmed in preparations of intestinal mucosa. Using a radioactively labeled inert marker, we found very short mean residence times of food particles in the gut of Cedar Waxwings (ca. 41 min). Because sucrose has to be hydrolyzed before it can be absorbed, the efficiency with which it is utilized may be hindered by the extremely fast passage rates in Cedar Waxwings. We suggest that the preference of Cedar Waxwings for monosaccharides over sucrose is due to the relative inefficiency of sucrose absorption. However, absorption efficiencies cannot explain the strong preference of glucose over fructose. In consequence, neither the caloric value of the sugars nor the absorption efficiency was adequate to explain the sugar preferences exhibited by Cedar Waxwings. We conclude that the preferences for simple sugars appear to be determined by the complex interaction between digestive constraints, postingestional effects, and taste. Received 19 January 1988, accepted 10 August 1988. THE disaccharide sucrose and the monosaccharide hexoses, fructose and glucose, are the most common simple sugars in fruit pulp and nectar (Chan and Kwok 1975; Baker and Baker 1983, 1986; Reid and Freeman MS). Hummingbird-pollinated plants produce nectars with a high proportion of sucrose whereas passerinepollinated plants produce nectars with a low proportion of sucrose and high proportion of hexoses (Cruden and Toledo 1977; Baker and Baker 1982, 1983). Small bird-dispersed fruits, which are typically consumed by passerines, contain mainly hexoses, whereas cultivated fruits used for human consumption tend to have high sucrose contents (Baker and Baker 1986, pers. comm.). These differences in sugar composition remain largely unexplained. It has been postulated that chemical characteristics of nectar and fruit pulp evolved in response to the 3Present address: Department of Zoology, University of Florida, Gainesville, Florida 32611 USA. preferences of pollinators and seed dispersers (Baker and Hurd 1968, Howell 1979, Levey 1987). With few exceptions (Hainsworth and Wolf 1976, Stiles 1976), the sugar preferences of birds that feed on nectar and fruit are unknown. Glucose, fructose, and sucrose have different modes of intestinal transport, and produce different metabolic effects after ingestion and absorption (Sestoft 1983). Even though they are similar chemically and in caloric value, these sweet substances may not be biologically equivalent. The European Starling (Sturnus vulgaris) rejects sucrose solutions but readily accepts solutions of fructose and glucose (Schuler, 1983). Sucrose aversion in the Starling is associated with a deficiency of the intestinal enzyme sucrase which hydrolyzes sucrose into fructose and glucose (Martinez del Rio et al. 1988). Animals that lack sucrase cannot digest and absorb sucrose. Consequently, the presence of undigested sucrose in the intestine of these animals can cause severe osmotic diarrhea. In this way, 64 The Auk 106: 64-71. January 1989 This content downloaded from 207.46.13.20 on Tue, 27 Dec 2016 17:57:48 UTC All use subject to http://about.jstor.org/terms January 1989] Sugar Preferences in Cedar Waxwings 65 the absence of intestinal sucrase can be associated with aversion for sucrose (Sunshine and Kretchmer 1964). We studied the sugar preferences of the Cedar Waxwing (Bombycilla cedrorum), one of the most heavily frugivorous birds in temperate North America (Martin et al. 1951), and analyzed the influence of taste and postingestional factors on these preferences. Because most birddispersed fruits in temperate North America are hexose-dominated (I. Baker and H. G. Baker in litt.), we predicted that Cedar Waxwings would prefer glucose and fructose over sucrose. We also hypothesized that this preference would be a result of sucrase deficiency. We examined these hypotheses by simple choice tests; by estimating the efficiency with which the birds digested and absorbed sucrose, glucose, and fructose in vivo; and by assaying for sucrase in preparations of intestinal mucosa.

Structural analysis of the nontoxic lipid A of Rhodobacter capsulatus 37b4.

Abstract: Lipid A from Rhodobacter capsulatus 37b4 consists of a d-glucosaminyl-(β1–6)-d-glucosamine disaccharide backbone, carrying diphosphorylethanolamine at C-1 of the reducing glucosamine and phosphorylethanolamine at C-4′ of the nonreducing glucosamine. 1,4′-Bisphosphorylated lipid A, lacking the polar head groups, was also encountered and contributed to the observed microheterogeneity in the phosphate substitution. The amino functions of both glucosamines are substituted almost entirely by the rare 3-oxotetradecanoic acid, which is a characteristic constituent of lipid A in the genus Rhodobacter. 3-Hydroxydecanoic acid is ester-bound at C-3 and C-3′ of the glucosamine disaccharide and the one at the nonreducing glucosamine (C-3′) is partially substituted by dodecenoic acid to form an ester-bound diester. In free lipid A, hydroxy groups at C-4 and C-6′ of the glucosamine disaccharide are unsubstituted, C-6′ being the putative attachment point of the lipopolysaccharide core. The nontoxic Rhodobacter capsulatus lipid A shows extensive serological cross-reaction with the toxic Salmonella lipid A. Structural similarities in the hydrophilic part of both types of lipid A, dissimilarities in the hydrophobic part and their impacts on serologic properties are discussed.

Synthese und Eigenschaften von Kohlenhydrattensiden

Abstract: Synthese d'O-alkyl glycosides a partir de mono ou polysaccharides et d'alcools gras. Etude de leur activite superficielle

Kinetics, equilibria, and modeling of the formation of oligosaccharides from D‐glucose with Aspergillus niger glucoamylases I and II

Abstract: Near-homogeneous forms of glucoamylases I and II, previously purified from an industrial Aspergillus niger preparation, were incubated with D-glucose at a number of temperatures and pH values. Kinetics and equilibria of the formation of alpha,beta-trehalose, kojibiose, nigerose, maltose, isomaltose, panose, and isomaltotriose, which with isomaltotetraose were the only products formed, were determined. There was no difference in the abilities of GA I and GA II to form these products. Activation energies for the formation of maltose and panose were lower than those of the other Oligosaccharides. Relative rates of oligosaccharide production based on glucoamylase hydrolytic activity did not vary significantly between pH 3.5 and 4.5 but were lower at pH 5.5. Maltose was formed much faster than any other product. Equilibrium concentrations at higher dissolved solids concentrations decreased in the order isomaltose, isomaltotriose, kojibiose, nigerose, maltose, alpha, beta-Mrehalose, panose, and isomaltotetraose. They were not appreciably affected by changes in temperature or pH. A kinetic model based on adsorption of D-glucose and the seven di- and trisaccharides by the first three glucoamylase subsites was formulated. Oligosaccharide formation was simulated with the model, using equilibrium data gathered for this article and subsite binding energies and kinetic parameters for oligosaccharide hydrolysis measured earlier. Agreement of simulated and actual oligosaccharide formation data through the course of the reaction was excellent except at very high solid concentrations.

Solution conformation of sialosylcerebroside (GM4) and its NeuAc(α2→3)Galβ sugar component

Abstract: The solution conformations of GM4 ganglioside [NeuAc(α23)Gal(β1)Cer] in (2H3C)2SO and its component disaccharide in 2H2O were investigated with the aid of 1H-nuclear magnetic resonance spectroscopy (nuclear Overhauser effect, analysis of coupling constants) and by energy-minimum calculations. The existence of three low-energy conformers obtained by theoretical calculations was supported by experimental findings in the case of GM4, whereas the disaccharide appears to exist as a mixture of two conformers.

Eremomycin--new glycopeptide antibiotic: chemical properties and structure.

Abstract: By a combination of chemical and spectroscopic (1H and 13C NMR) studies the structure of a glycopeptide antibiotic eremomycin has been elucidated. It is closely related to vancomycin, but differs in sugar and chlorine content. The eremomycin aglycone contains monodechlorovancomycinic acid; the only chlorine atom is situated in the second amino acid after the N-terminal amino acid residue of the peptide. The sugar part is composed of glucose and two residues of an amino sugar shown to be 2, 3, 6-trideoxy-3-amino-C-3-methyl-L-arabino-hexopyranose (4-epi-vancosamine). One of the amino sugar residues is a component of the disaccharide 2-O-(α-L-4-epi-vancosaminyl)-β-Dglucopyranose, attached to a triphenyl ether moiety; the position of another one is at the serine oxygen in the C-terminal region of the aglycone.

Synthesis of mono- and disaccharide amino-acid derivatives for use in solid phase peptide synthesis.

Abstract: N-Fluorenylmethyloxycarbonyl-protected serine and threonine derivatives, carryingO-glycosidically α- or β-linked peracetylated β-d-Galp-(1–3)-d-GalNAcp carbohydrate chains, were prepared. These derivatives are intended for use in solid phase glycopeptide synthesis. Suitably protected mono- and disaccharide thioglycosides were used as carbohydrate intermediates. These were activated by treatment with bromine to give the glycosyl bromides, which were then used in silver triflate-promoted glycosidations ofN-fluorenylmethyloxycarbonyl amino-acid phenacyl esters. Removal of the phenacyl esters with zinc gave the target free acids.

Kinetics of the hydrolysis of di- and trisaccharides with Aspergillus niger glucoamylases I and II.

Abstract: Near-homogeneous forms of glucoamylases I and II, previously purified from an industrial Aspergillus niger preparation, were used to hydrolyze a number of di- and trisaccharides linked by alpha-D-glucosidic bonds. Maximum rates and Michaelis constants were obtained at various temperatures and pH values with glucoamylase I for the disaccharides beta,alpha-trehalose, kojibiose, nigerose, maltose, and isomaltose and the trisaccharides panose and iso-maltotriose, and with glucoamylase II for maltose, maltotriose, and isomaltotriose. Maximum rates were highest and energies of activation were lowest for maltose, maltotriose, and panose, the only three substrates containing alpha-D-(1, 4)-glucosidic bonds. Michaelis constants were lowest and standard heats of binding were most negative for maltose and maltotriose. The variation of maximum rates and Michaelis constants with varying pH values suggested that two carboxyl groups were involved in substrate binding.

Poly(vinylsaccharide)s, 5. Synthesis and characterization of poly(vinylsaccharide)s of the amide type with disaccharides in the side chain

Abstract: The synthesis of well-defined monovinylsaccharide monomers containing disaccharide units is described. Four different monomers, N-disaccharide-substituted acryl- and methacrylamides, were prepared and polymerized to the corresponding polymers by free-radical polymerization in aqueous solution using different initiator systems. The influence of the structural differences of the disaccharide units on the solution properties was studied by viscosity and light scattering measurements. A comparison with known poly(vinylsaccharide)s with monosaccharides in the side chain is made.

Experimental characterization of the autophagic-lysosomal pathway in isolated rat hepatocytes.

Abstract: When isolated rat hepatocytes are incubated under amino-acid-free conditions autophagy is maximally activated and overall lysosomal proteolysis is greatly enhanced. To facilitate this, cytoplasmic material is sequestered by autophagic membranes, and the resulting autophagosomes enter the lysosomes by a fusion process to have their contents degraded. The various steps in the autophagic-lysosomal pathway have been investigated by utilizing reversible electropermeabilization to introduce radioactive sugar probes into the hepatocyte cytosol. The inert disaccharide sucrose and the inert trisaccharide raffinose have been used as sequestration probes to study the sequestrational step of autophagy, while the hydrolysable disaccharide lactose has been used to study the fusion and intralysosomal hydrolysis steps. Sucrose and lactose have been used to map the extent of convergence between the autophagic and endocytic (heterophagic) pathways. Sequestration of native cytosolic enzymes has been measured to investigate the question of selectivity in the autophagic process. Finally, the effect of insulin on the sequestrational step has been evaluated.

New lysosphingolipid derivatives

Abstract: Novel derivatives of lysophingolipids free from sialic acids which are N-acyllysosphingolipids having one of the two formulae: in which -A- stands for the group -CH=CH- or -CH₂-CH₂-, n₁ is a whole number of between 6 and 18, n₂ a whole number of between 11 and 15, X is a hydrogen atom or the residue of a monosaccharide or a disaccharide or phosphorylcholine and R represents an alkyl radical derived from a saturated or unsaturated aliphatic carboxylic acid having from 2 to 24 carbon atoms substituted by one or more polar groups. The lysosphingolipid derivatives of the invention exhibit an inhibiting action on protein-kinase C activation and, thus, can be utilized in therapies for various pathologies of the nervous system.