Malvidin 3-rutinoside as the pigment responsible for bract color in Curcuma alismatifolia.
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Malvidin 3-rutinoside was the only anthocyanin identified from pink bracts of Curcuma alismatifolia cultivars. The concentration of malvidin 3-rutinoside in three cultivars increased as the intensity of the pink color in the bracts increased. (+info)
Structure/thermodynamics relationships of lectin-saccharide complexes: the Erythrina corallodendron case.
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Molecular dynamics (MD) simulations of Erythrina corallodendron lectin binding to a monosaccharide, alpha-galactose, and a disaccharide, N-acetyl lactosamine, have been performed in order to investigate the relationship between structure and thermodynamics. A simulated annealing protocol has been used to generate ensembles of structures for the two complexes, from which both qualitative and quantitative information on binding dynamics have been extracted. The ensembled averaged lectin-saccharide interaction enthalpy is equivalent for both sugars, whereas the calculation based on the X-ray structures does show a difference. Within large statistical errors, the calculated 'binding enthalpy' is also the same for the two systems. These errors arise largely from terms involving solvent and are a typical limitation of current MD simulations. Significant qualitative differences in binding between the two complexes are, however, observed over the ensembles. These could be important for unraveling the structure/thermodynamic relationship. Stated simply, there are a greater number of binding options available to the disaccharide compared to the monosaccharide. The implications of alternative binding states on thermodynamic parameters and the 'breaking of enthalpy-entropy compensation' are discussed. The role of solvent in lectin-saccharide complex formation is suggested to be significant. (+info)
Glucose and disaccharide-sensing mechanisms modulate the expression of alpha-amylase in barley embryos.
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The aim of this study was to investigate the sugar-sensing processes modulating the expression of alpha-amylase in barley (Hordeum vulgaris L. var Himalaya) embryos. The results highlight the existence of independent glucose (Glc) and disaccharides sensing. Glc treatment destabilizes the alpha-amylase mRNA. Non-metabolizable disaccharides repress alpha-amylase induction, but have no effects on transcript stability. Structure-function analysis indicates that a fructose (Fru) moiety is needed for disaccharide sensing. Lactulose (beta-galactose [Gal][1-->4]Fru), palatinose (Glc[1-->6]Fru), and turanose (Glc[1-->3]Fru) are not metabolized but repress alpha-amylase. Disrupting the fructosyl moiety of lactulose and palatinose, or replacing the Fru moiety of beta-Gal[1-->4]Fru with Glc or Gal results in molecules unable to repress alpha-amylase. Comparison of the molecular requirements for sucrose transport with those for disaccharide sensing suggests that these sugars are perceived possibly at the plasma membrane level independently from sucrose transport. (+info)
Intracellular inhibition of blood group A glycosyltransferase.
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We report the intracellular inhibition of blood group A N-acetylgalactosaminyltransferase in the human colorectal carcinoma cell line HT29 by 3-amino-3-deoxy-[Fucalpha(1-2)]Galbeta-O(CH2)7CH3. Inhibition was demonstrated with a novel capillary electrophoresis assay that monitored decreased intracellular conversion of fluorescently labelled Fucalpha(1-2)Gal-R acceptor to the corresponding A epitope, GalNAcalpha(1-3)[Fucalpha(1-2)]Galbeta-R. Growth of HT29 cells with either the amino-inhibitor or a competitive substrate, Fucalpha(1-2)Galbeta-O(CH2)7CH3, also resulted in decreased expression of blood group A determinants on cell-associated glycoproteins, as detected by immunoprecipitation analysis using A-specific monoclonal antibodies. Furthermore, exposure of these cells to the amino-inhibitor or competitive substrate resulted in significant reduction of cell-surface expression of blood group A determinants. As integrin alpha3beta1, a cell-surface receptor mediating cell-cell and cell-extracellular matrix interactions, was shown previously to be a major carrier of blood group A determinants on HT29 cells, the studies described herein highlight the potential usefulness of these compounds for elucidating the role of blood group A determinants in biological phenomena. (+info)
Chemical analysis of the developmental pattern of polysialylation in chicken brain. Expression of only an extended form of polysialyl chains during embryogenesis and the presence of disialyl residues in both embryonic and adult chicken brains.
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Recent studies have demonstrated the involvement of two polysialyltransferases in neural cell adhesion molecule (N-CAM) polysialylation. The availability of cDNAs encoding these enzymes facilitated studies on polysialylation of N-CAM. However, there is a dearth of detailed structural information on the degree of polymerization (DP), DP ranges, and the influence of embryogenesis on the DP. It is also unclear how many polysialic acid (polySia) chains are attached to a single core N-glycan. In this paper we applied new, efficient, and sensitive high pressure liquid chromatography methods to qualitatively and quantitatively analyze the polySia structures expressed on embryonic and adult chicken brain N-CAM. Our studies resulted in the following new findings. 1) The DP of the polySia chains was invariably 40-50 throughout developmental stages from embryonic day 5 to 21 after fertilization. In contrast, glycopeptides containing polySia with shorter DPs, ranging from 15 to 35, were isolated from adult brain. 2) Chemical evidence showed glycan chains abundant in Neu5Acalpha2,8Neu5Ac were expressed during all developmental stages including adult. 3) Levels of both di- and polySia were found to show distinctive changes during embryonic development. (+info)
Chitin catabolism in the marine bacterium Vibrio furnissii. Identification, molecular cloning, and characterization of A N, N'-diacetylchitobiose phosphorylase.
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The major product of bacterial chitinases is N,N'-diacetylchitobiose or (GlcNAc)(2). We have previously demonstrated that (GlcNAc)(2) is taken up unchanged by a specific permease in Vibrio furnissii (unlike Escherichia coli). It is generally held that marine Vibrios further metabolize cytoplasmic (GlcNAc)(2) by hydrolyzing it to two GlcNAcs (i.e. a "chitobiase "). Here we report instead that V. furnissii expresses a novel phosphorylase. The gene, chbP, was cloned into E. coli; the enzyme, ChbP, was purified to apparent homogeneity, and characterized kinetically. The DNA sequence indicates that chbP encodes an 89-kDa protein. The enzymatic reaction was characterized as follows. (GlcNAc)(2)+P(i) GlcNAc-alpha-1-P+GlcNAc K'(cq)=1.0+/-0.2 Reaction 1 The K(m) values for the four substrates were in the range 0.3-1 mm. p-Nitrophenyl-(GlcNAc)(2) was cleaved at 8.5% the rate of (GlcNAc)(2), and p-nitrophenyl (PNP)-GlcNAc was 36% as active as GlcNAc in the reverse direction. All other compounds tested displayed +info)
The chitin disaccharide, N,N'-diacetylchitobiose, is catabolized by Escherichia coli and is transported/phosphorylated by the phosphoenolpyruvate:glycose phosphotransferase system.
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We have previously reported that wild type strains of Escherichia coli grow on the chitin disaccharide N,N'-diacetylchitobiose, (GlcNAc)(2), as the sole source of carbon (Keyhani, N. O., and Roseman, S. (1997) Proc. Natl. Acad. Sci., U. S. A. 94, 14367-14371). A nonhydrolyzable analogue of (GlcNAc)(2,) methyl beta-N, N'-[(3)H]diacetylthiochitobioside ([(3)H]Me-TCB), was used to characterize the disaccharide transport process, which was found to be mediated by the phosphoenolpyruvate:glycose phosphotransferase system (PTS). Here and in the accompanying papers (Keyhani, N. O., Boudker, O., and Roseman, S. (2000) J. Biol. Chem. 275, 33091-33101; Keyhani, N. O., Bacia, K., and Roseman, S. (2000) J. Biol. Chem. 275, 33102-33109; Keyhani, N. O., Rodgers, M., Demeler, B., Hansen, J., and Roseman, S. (2000) J. Biol. Chem. 275, 33110-33115), we report that transport of [(3)H]Me-TCB and (GlcNAc)(2) involves a specific PTS Enzyme II complex, requires Enzyme I and HPr of the PTS, and results in the accumulation of the sugar derivative as a phosphate ester. The phosphoryl group is linked to the C-6 position of the GlcNAc residue at the nonreducing end of the disaccharide. The [(3)H]Me-TCB uptake system was induced only by (GlcNAc)(n), n = 2 or 3. The apparent K(m) of transport was 50-100 micrometer, and effective inhibitors of uptake included (GlcNAc)(n), n = 2 or 3, cellobiose, and other PTS sugars, i.e. glucose and GlcNAc. Presumably the PTS sugars inhibit by competing for PTS components. Kinetic properties of the transport system are described. (+info)
Isolation and characterization of IIAChb, a soluble protein of the enzyme II complex required for the transport/phosphorylation of N, N'-diacetylchitobiose in Escherichia coli.
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N,N'-Diacetylchitobiose is transported/phosphorylated in Escherichia coli by the (GlcNAc)(2)-specific Enzyme II permease of the phosphoenolpyruvate:glycose phosphotransferase system. IIA(Chb), one protein of the Enzyme II complex, was cloned and purified to homogeneity. IIA(Chb) and phospho-IIA(Chb) form stable homodimers (). Phospho-IIA(Chb) behaves as a typical epsilon2-N (i.e. N-3) phospho-His protein. However, the rate constants for hydrolysis of phospho-IIA(Chb) at pH 8.0 unexpectedly increased 7-fold between 25 and 37 degrees C and increased approximately 4-fold with decreasing protein concentration at 37 degrees C (but not 25 degrees C). The data were explained by thermal denaturation studies using CD spectroscopy. IIA(Chb) and phospho-IIA(Chb) exhibit virtually identical spectra at 25 degrees C (approximately 80% alpha-helix), but phospho-IIA(Chb) loses about 30% of its helicity at 37 degrees C, whereas IIA(Chb) shows only a slight change. Furthermore, the T(m) for thermal denaturation of IIA(Chb) was 54 degrees C, only slightly affected by concentration, whereas the T(m) for phospho-IIA(Chb) was much lower, ranging from 40 to 46 degrees C, depending on concentration. In addition, divalent cations (Mg(2+), Cu(2+), and Ni(2+)) have a dramatic and differential effect on the structure, depending on the state of phosphorylation of the protein. Thus, phosphorylation destabilizes IIA(Chb) at 37 degrees C, potentially affecting the monomer/dimer transition, which correlates with its chemical instability at this temperature. The physiological consequences of this phenomenon are briefly considered. (+info)